Mosk ransomware: what it is and how to remove it
Mosk is a cryptovirus that belongs to the infamous malware family Djvu - Stop. It is the 181st version that showed up in early November 2019.
Facts checked October 6, 2026. Removal steps tested on Windows 11 (26H2) and checked against Microsoft's and the browser makers' current documentation. Sections marked as our earlier report are the original text: they describe the threat as it was then and have not been reviewed since. The 2026 status, the removal steps and the questions are current.
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Mosk ransomware: summary
| Name | Mosk ransomware |
|---|---|
| Type | Cyprovirus |
| First spotted | Early November 2019 |
| Ransomware family | Mosk is a variant of Djvu/STOP ransomware strain |
| File extension | All personal files on a local hard drive and all connected networks/external drives are appended with .mosk extension |
| Ransom note | _readme.txt is placed into each of the infected files' folders and includes all the information about how victims should proceed next in order to recover the encrypted data |
| Removal | Scan the PC with security software to find and remove the malware and anything installed with it. Fortect scans Windows for malware and repairs the system files and settings it damaged. Remove it nowTo use the full-featured product, you have to purchase a license for Fortect. The scan is free. |
Show 16 more facts
| Contact | Hackers use salesrestoresoftware@firemail.cc or salesrestoresoftware@gmail.com – new email addresses that were not used in previous versions of Djvu |
|---|---|
| Ransom size | Ransomware authors ask for $980 in Bitcoin for file redemption. Users are also offered a 50% discount if the contact is made within 72 hours of the infection |
| File decryption | There are several ways that might be effecting when trying to decrypt .mosk encrypted files. Emsisoft Decryptor for STOP Djvu is one of the tools that can be used for offline encrypted files, although there are other methods available too – please check our recovery section for more details |
| Malware removal | Rely on anti-malware software to terminate the infection (entering Safe Mode might be necessary in some cases) |
| Detection names | No Microsoft detection name is known |
| Encrypted file extension | .mosk |
| Decryptor | No free decryptor is known for this variant; check No More Ransom (nomoreransom.org) for updates |
| Distribution | Not recorded in the old report |
| Damage | Not recorded in the old report |
| Symptoms | Files renamed with a new extension and a ransom note left in folders |
| Evidence | 5 write-ups by security sites; no sample analysed yet |
| Encrypted files | .mosk |
| Attacker contacts | salesrestoresoftware@firemail.cc |
| Free decryptor | No free decryptor is known (checked 6 October 2026) |
| First seen | 12 November 2019 |
| Facts checked | 6 October 2026 |
- File extension:
.mosk - Note file:
_readme.txt - Contact:
salesrestoresoftware@firemail.cc
From our report of Nov 2019 · not reviewed since
More from our earlier report on Mosk ransomware
- Ransomware might render your Windows OS unstable.
How Mosk ransomware behaves
From our report of Nov 2019 · not reviewed since
Mosk is ransomware that restricts access to personal files and then demands around $1000 ransom for their redemption
Mosk is a cryptovirus that belongs to the infamous malware family Djvu - Stop.
It is the 181st version that showed up in early November 2019. The main purpose of this ransomware is to hold pictures, videos, and other files hostage, and only release the decryption software if victims agree to pay either $980 or $490 in Bitcoin.
Users infected with Most ransomware find out about the demands in a ransom note which is called _readme.txt. The file is dropped into every single folder where the encrypted data (marked with .mosk appendix) is located.
According to research, Mosk ransomware encrypts data with Salsa20 or another strong cipher, preventing users from accessing it. While there is no guaranteed way to decrypt encrypted files without paying, experts advise staying away from criminals and not contacting them via salesrestoresoftware@firemail.cc or salesrestoresoftware@gmail.com emails. Make sure you check updates for StopDecrypter. Also, Emsisoft Decryptor should also be checked if dealing with this ransomware virus.
The ransomware family that Mosk virus belongs to became one of the most prominent ones in the past year, and new versions are being released by cybercriminals on a regular basis. Most recently, security experts from Emsisoft released a decryptor that worked for 148 variants, and users who are affected by those (older versions, such as Peta, Hese, Nasoh, etc.) could get their data for free.
Unfortunately, Mosk ransomware is one of the newer variants of the malware, so its decryption might not be currently possible. Nevertheless, malware researchers also created an alternative tool that might work for victims whose data was encrypted with offline keys. Additionally, if you refer to the recovery section of this article, you will find other methods that might be helpful to decrypt Mosk ransomware files.
Nevertheless, before you proceed, you should remove Mosk ransomware from your machine. For that, you should rely on reputable anti-malware for the process, such as , , although you can pick other removal software of your choice and perform a full system scan in Safe Mode. To resume normal operations with your Windows computer post-infection and prevent system crashes due to corrupted or broken system files, try using .
Note that the malware might load secondary modules or payloads in order to perform malicious activities like keystroke logging and data harvesting. Therefore, Mosk ransomware removal should be performed as soon as possible.
From our report of Nov 2019 · not reviewed since
The operation of Mosk ransomware and file encryption process
Ransomware is a type of malware that is usually designed for Windows operating systems, and Mosk ransomware is not an exception - it affects Windows 10, 8, 7, and older versions of the OS. Additionally, unlike most other malware, cryptoviruses do not try to hide from victims after the infection process is initiated.
Before encrypting data, however, the Mosk virus makes several changes to the host system. Once the malicious executable (the name of which is randomly generated) is downloaded, it is placed into one of the following locations:
The malicious file is then executed - it starts the preparations from the file encryption process (Windows registry modified, Windows backup function disabled, connections to remote servers established, etc.).
Once all personal files are locked on the computer, the ransom note _readme.txt is dropped, which reads:
Keep in mind that paying ransom to Mosk ransomware developers is quite risky - they might simply ignore your requests after you pay the demanded ransom. Additionally, payments from victims will only fuel their will to produce more robust versions of Djvu and infect more victims.
Remember to remove Mosk ransomware along with all the secondary payloads on your PC - check out the details on how to enter Safe Mode (might be necessary sometimes due to prevalence features of the malware) in the removal section of the post below.
- %Temp%;
- %AppData%;
- %LocalAppData%
From our report of Nov 2019 · not reviewed since
Mosk ransomware authors rely on pirated software installers for the infection
Djvu/STOP is one of the largest ransomware families to date, and is extremely prevalent - it accounts for 56% of total infections around the globe, according to Emsisoft's ransomware report for 2019 Q2 - Q3. Mosk ransomware developers managed to achieve such success due to active distribution campaigns, that are usually performed via torrent/warez websites that host pirated software installers or keygens/cracks that can activate paid versions of programs for free.
While security experts warn users that downloading such files is not only illegal but also dangerous due to potential malware infections, there will still be many that are willing to risk it. In order to avoid devastating consequences, users should take precautions when downloading high-risk files from unsafe sites (we do not endorse users engaging in pirating software in the first place).
You should employ an ad-blocker extension that would block malicious JavaScript from being executed while visiting torrent and similar sites. Additionally, you should always scan the executable via tools like Virus Total before proceeding to open it. Nevertheless, due to its functionality (i.e., cracking), keygens and cracks will always be marked as malicious, regardless if they include a malicious payload that carries ransomware or not.
Also, you should make sure that you equip your computer with robust anti-malware software, update your OS/programs on time, not open attachments from spam emails, back up your files, and practice general caution when it comes to online web browsing.
The Mosk ransomware note
ATTENTION!
Don't worry, you can return all your files!
All your files like photos, databases, documents and other important are encrypted with strongest encryption and unique key.
The only method of recovering files is to purchase decrypt tool and unique key for you.
This software will decrypt all your encrypted files.
What guarantees you have?
You can send one of your encrypted file from your PC and we decrypt it for free.
But we can decrypt only 1 file for free. File must not contain valuable information.
You can get and look video overview decrypt tool:
https://we.tl/t-IbdGyCKhdr
Price of private key and decrypt software is $980.
Discount 50% available if you contact us first 72 hours, that's price for you is $490.
Please note that you'll never restore your data without payment.
Check your e-mail "Spam" or "Junk" folder if you don't get answer more than 6 hours.
To get this software you need write on our e-mail:
salesrestoresoftware@firemail.cc
Reserve e-mail address to contact us:
salesrestoresoftware@gmail.com
How to remove Mosk ransomware
Tools you'll need
All of these are free except where noted. Download them on a clean device if the infected PC is offline.
- A USB stick: to keep the ransom note, two or three encrypted files and screenshots off the infected PC.
- Microsoft Defender Offline: built into Windows 11 and Windows 10; scans before Windows starts, so running malware cannot hide.
- Microsoft Safety Scanner: a second, portable scanner with current signatures; each download works for 10 days.
- ID Ransomware: identifies the family from the note and one encrypted file and says whether a decryptor exists.
- No More Ransom: the free decryptors from police and security companies; check it again every few months.
- Fortect (optional): scans Windows for malware and repairs the system files and settings it damaged. The free scan is in the box above.
How to remove Mosk ransomware and get your files back
Work in this order.
Disconnecting comes first, removal comes before any restore, and nothing here asks you to contact the attackers.
Step 1: Disconnect the PC and unplug backup drives
Unplug the network cable or turn off Wi-Fi, and disconnect USB drives, external disks and network shares, so Mosk ransomware cannot reach more files. Pause OneDrive, Google Drive or Dropbox sync, because synced folders upload the encrypted copies over the good ones.
Leave the PC on but offline while you read the next steps, since a restart can let the ransomware run again. This applies to Windows 11 and Windows 10 alike.
Windows 11: turn off Wi-Fi to take the PC offline. Full procedure with screenshots: Ransomware: first steps, finding a decryptor and recovering files
Step 2: Save the ransom note and confirm the family
Your files now end in
.moskand the instructions are in_readme.txt. Save both to a USB stick, a copy of the note and two small encrypted files, before anything else.On another device, check them with ID Ransomware or Crypto Sheriff: the family name decides which decryptor, if any, can help. Keep the note's ID and contact line for your report.
Windows 11: the ransom note and encrypted files to copy for identification. Full procedure with screenshots: Ransomware: first steps, finding a decryptor and recovering files
Step 3: Check for a free decryptor
Our last check found that for Mosk ransomware, no free decryptor is known (checked 6 October 2026). Look again yourself in the No More Ransom list and the free decryptor pages of Emsisoft, Avast and Kaspersky, which add new families every year.
A decryptor needs the ransomware gone first, or it encrypts the files again. Keep at least one copy of the encrypted files on an external drive, even if no tool works yet.
Full procedure with screenshots: Ransomware: first steps, finding a decryptor and recovering files
Step 4: Remove the ransomware before you restore or decrypt
Removing Mosk ransomware does not bring the files back, but it has to come first. Start with Defender's Full scan, then the offline scan from the same Scan options page, which checks the disk before Windows loads.
If the scan cannot start, use Safe Mode with Networking. Delete the ransom notes only after you have saved a copy, because removal tools sometimes leave them behind on Windows 11 and Windows 10.
Windows 11: Windows Security > Virus & threat protection > Scan options. Full procedure with screenshots: Run a Microsoft Defender Offline scan
Step 5: Look for shadow copies of the files
Windows keeps shadow copies for restore points and backups, and some ransomware fails to delete them.
vssadmin list shadowsin an administrator Command Prompt tells you at once whether any exist.If they do, right-click the folder that held your files, open Properties > Previous Versions, select a version from before the attack, and click Open to check it before you Restore or copy the files out. Windows 11 and Windows 10 both have the tab.
Windows 11: vssadmin list shadows shows whether shadow copies exist. Full procedure with screenshots: Ransomware: first steps, finding a decryptor and recovering files
Step 6: Restore the files from a backup or recover deleted originals
A backup made before the attack is the surest way back. Connect it only once the PC is clean, then restore from File History, Windows Backup, OneDrive's Restore your OneDrive or your own external copies.
Without a backup, try file recovery: the originals that Mosk ransomware deleted may still be on the disk until something overwrites them. Install nothing new on the drive you want to recover from on the Windows 11 or Windows 10 PC.
Full procedure with screenshots: Recover deleted files (Recycle Bin, backups, OneDrive) On uGetFix
Instructions for each browser and system
The detailed steps for every browser and system this guide covers. Open the one you use.
Manual removal using Safe Mode
Important! →
Manual removal guide might be too complicated for regular computer users. It requires advanced IT knowledge to be performed correctly (if vital system files are removed or damaged, it might result in full Windows compromise), and it also might take hours to complete. Therefore, we highly advise using the automatic method provided above instead.
Step 1. Access Safe Mode with Networking
Manual malware removal should be best performed in the Safe Mode environment.
Windows 7 / Vista / XP
- Click Start > Shutdown > Restart > OK.
- When your computer becomes active, start pressing F8 button (if that does not work, try F2, F12, Del, etc. - it all depends on your motherboard model) multiple times until you see the Advanced Boot Options window.
- Select Safe Mode with Networking from the list.
Windows 10 / Windows 8
- Right-click on Start button and select Settings.
- Scroll down to pick Update & Security.
- On the left side of the window, pick Recovery.
- Now scroll down to find Advanced Startup section.
- Click Restart now.
- Select Troubleshoot.
- Go to Advanced options.
- Select Startup Settings.
- Press Restart.
- Now press 5 or click 5) Enable Safe Mode with Networking.
Step 2. Shut down suspicious processes
Windows Task Manager is a useful tool that shows all the processes running in the background. If malware is running a process, you need to shut it down:
- Press Ctrl + Shift + Esc on your keyboard to open Windows Task Manager.
- Click on More details.
- Scroll down to Background processes section, and look for anything suspicious.
- Right-click and select Open file location.
- Go back to the process, right-click and pick End Task.
- Delete the contents of the malicious folder.
Step 3. Check program Startup
- Press Ctrl + Shift + Esc on your keyboard to open Windows Task Manager.
- Go to Startup tab.
- Right-click on the suspicious program and pick Disable.
Step 4. Delete virus files
Malware-related files can be found in various places within your computer. Here are instructions that could help you find them:
- Type in Disk Cleanup in Windows search and press Enter.
- Select the drive you want to clean (C: is your main drive by default and is likely to be the one that has malicious files in).
- Scroll through the Files to delete list and select the following:
Temporary Internet Files
Downloads
Recycle Bin
Temporary files - Pick Clean up system files.
- You can also look for other malicious files hidden in the following folders (type these entries in Windows Search and press Enter):
%AppData%
%LocalAppData%
%ProgramData%
%WinDir%
After you are finished, reboot the PC in normal mode.
From our report of Nov 2019 · not reviewed since
Mosk ransomware removal and file recovery methods
Ransomware is a sophisticated computer parasite that includes many features and enables multiple background changes.
For that reason, manual Mosk ransomware removal is almost impossible for regular computer users - we do not recommend to engage in doing so. Instead, there are several security programs capable of removing malware automatically after a full system scan is performed.
Be aware that malware removal from the system might result in permanent data corruption. Nevertheless, if the payload is kept on the system running, all the incoming files will be encrypted, making the computer practically unusable.
Thus, we advise you to remove Mosk ransomware with anti-malware software. Due to advanced functionality of the virus, that might not be possible until you enter Safe Mode and perform a full system scan from there - the guidelines below. Once you terminate the virus, you can try using several different methods to recover .mosk locked files, as there are several decryptors and third-party tools available for the disposal.
[GI=method-1]To get rid of Mosk ransomware infection, enter Safe Mode with Networking as described below and perform a full system scan with anti-malware:
[GI=method-2]System Restore is another option when trying to get rid of the virus:
Data recovery software recovers working copies of lost files from the dedicated hard drive locations. Nevertheless, it only works if that location was not filled with new information since ransomware infection. Thus, while full data recovery might not be possible, this method might restore at least some of your files.
Windows Previous Versions feature might prove useful when trying to restore encrypted files
This solution might be effective if you had System Restored feature enabled before ransomware struck your computer.
ShadowExplorer solution might be right for you
Ransomware is programmed to delete shadow volume copies. If that process fails, you have a chance of restoring files from automated Windows backups with ShadowExplorer.
Try Emsisoft's decryptor and Dr.Web service
Mosk ransomware file decryption highly depends on various factors; for example, whether the malware managed to contact its Command & Control servers. Thus, try these methods:
- Emsisoft Decryptor for STOP Djvu might be useful if the encryption was performed offline
- Contact Dr.Web for decryption service - recovery of certain file types (such as MS Office) might be possible. Note, service is not free)
Report it and recover your files
Report it
Report the attack even if you do not expect the files back: insurers and banks ask for the report number, and police use the contacts in the note to link cases.
- United States
- FBI IC3 · FTC ReportFraud
- United Kingdom
- Report Fraud (formerly Action Fraud) · NCSC
- Australia
- ReportCyber (ASD)
- EU countries
- Europol: national reporting sites
Give the victim ID, the note and the date the files were encrypted. A business that holds personal data may also have to notify its data protection authority, in the EU within 72 hours.
Make the next attack harmless
Mosk ransomware could only hurt the files that had no second copy, and the signs (files that end in .mosk and no longer open) showed exactly which ones those were.
The 3-2-1 rule fixes that:
- three copies
- two media
- one disconnected
A practical version for a home PC: OneDrive or another cloud backup with version history, plus an external disk that you plug in once a week for File History and then unplug. Test a restore now and then by opening a few files from the backup on another device.
Details, schedules and what not to back up are in our 3-2-1 backup guide for Windows.
Protect your privacy - employ a VPN
There are several ways how to make your online time more private - you can access an incognito tab.
However, there is no secret that even in this mode, you are tracked for advertising purposes. There is a way to add an extra layer of protection and create a completely anonymous web browsing practice with the help of VPN. This software reroutes traffic through different servers, thus leaving your IP address and geolocation in disguise.
Besides, it is based on a strict no-log policy, meaning that no data will be recorded, leaked, and available for both first and third parties. The combination of a secure web browser and VPN will let you browse the Internet without a feeling of being spied or targeted by criminals.
No backups? No problem. Use a data recovery tool
If you wonder how data loss can occur, you should not look any further for answers - human errors, malware attacks, hardware failures, power cuts, natural disasters, or even simple negligence.
In some cases, lost files are extremely important, and many straight out panic when such an unfortunate course of events happen. Due to this, you should always ensure that you prepare proper data backups on a regular basis.
If you were caught by surprise and did not have any backups to restore your files from, not everything is lost. is one of the leading file recovery solutions you can find on the market - it is likely to restore even lost emails or data located on an external device.
Questions about Mosk ransomware
How do I open .mosk files?
You cannot open them by renaming or with another program, because the content of files ending in .mosk has been encrypted. The only ways back are a working decryptor for the family, or clean copies from elsewhere:
- OneDrive versions
- File History
- an offline backup drive
- Previous Versions if the ransomware did not delete them
Identify the family first by uploading the ransom note and one encrypted file to ID Ransomware or No More Ransom. Avoid websites and programs that promise to open any encrypted file; they do not work and some are scams.
Is there a free Mosk ransomware decryptor?
We last checked on 6 October 2026, and for Mosk ransomware no free decryptor is known. We check No More Ransom, which collects free tools from police and security companies, and the decryptor pages of the major antivirus vendors. A working decryptor exists only when the encryption has a flaw or the keys were leaked or seized.
Ignore sites and videos that offer a "Mosk ransomware decryptor" for download or for a fee: these are usually scams or malware. Real decryptors are free and come from known security companies or law enforcement. Keep the encrypted files in case a tool appears later.
Should I pay the ransom?
We advise against it, and so do the FBI, Europol and national cyber agencies. Payment does not guarantee a working tool: some attackers never reply, some tools damage files, and some variants have no decryptor at all. Paying also funds further attacks and can make you a target again.
Before considering payment, try every recovery option in this guide and report the attack. Companies must involve their legal adviser and insurer, because payments to sanctioned groups can be illegal. If files are truly irreplaceable, store the encrypted copies and wait; decryptors sometimes appear later.
Can a data-recovery company decrypt my files for a fee?
Only if a decryptor already exists or the company pays the attackers for you. Some "ransomware recovery" services advertise that they can decrypt families with no known flaw; in practice they negotiate with the attackers and add their own fee. Others use the same free tools listed on No More Ransom.
Before you hire anyone, ask in writing how they will recover the files, whether they will contact the attackers and what happens if they fail. A legitimate service answers clearly. If a free decryptor exists for your family, you can run it yourself.
How did Mosk ransomware get on my computer?
The way Mosk ransomware spreads has not been documented yet, so look at your own recent activity. On home PCs, ransomware most often comes with cracked programs, game cheats, key generators and fake updates, or with an e-mail attachment that was opened. On business networks, attackers usually log in through Remote Desktop with a stolen or guessed password.
Think back to what was downloaded or installed in the days before files that end in .mosk and no longer open, and check the Downloads folder and Installed apps sorted by date. Keep anything suspicious for your report, but do not run it again.
Did Mosk ransomware steal my files or passwords?
We do not know yet. Nothing published so far shows data theft by Mosk ransomware, but the only confirmed sign is files that end in .mosk and no longer open, which says nothing about what happened before. Many current ransomware attacks copy files or run a password stealer first, so it is wise to act as if they did.
From a clean device, change the passwords that were saved in the browsers on this PC, starting with e-mail and banking, sign out of all sessions and turn on two-step verification. Watch bank statements and account activity for the next few weeks.
Is Mosk ransomware the same as other ransomware with a similar name?
Not necessarily. Ransomware names come from the file extension, the note or a word in the code, so unrelated families often end up with similar names, and one family can appear under several names. The difference matters: a decryptor or advice for one family does not fit another and can damage files.
Compare the ending added to your files and the exact name of the note with the summary table at the top of this guide, then upload the note and one encrypted file to ID Ransomware from a clean device. If the result names another family, follow the guide for that family instead.
Can I delete _readme.txt?
Yes, the note itself is harmless text and deleting it does not affect your files. Keep at least one copy first, outside the infected PC. _readme.txt contains your personal ID and the attackers' contact details, which identification services use to tell which family encrypted your files, and which a decryptor may need later.
Police reports also ask for it. Once you have saved a copy, you can remove the notes from every folder after the ransomware program has been removed and your files are restored or backed up.
Should I reinstall Windows after the .mosk attack?
Reinstalling removes the ransomware but not the encryption: your files ending in .mosk stay encrypted afterwards. So first copy the encrypted files and the ransom note to a separate drive, in case a decryptor appears later. Then decide:
- a clean-up with an offline scan is often enough for home PCs
- while a full reset is safer if remote access was involved
- scans keep finding new items
Restore your backups only after the PC is clean, and change passwords from another device.
Will Fortect remove Mosk ransomware?
Fortect scans Windows for malware and unwanted programs and repairs the system files and settings they change, and its free scan shows what it finds on your PC before you decide anything.
For Mosk ransomware, follow the plan above as well: the browser steps take back permissions and settings that no scanner treats as a threat, and uninstalling the program that brought it removes the source.
Run Microsoft Defender's full scan and, if anything was found, its offline scan as a second opinion. If the symptoms are gone after the plan and both scans are clean, there is nothing more to do.
Sources
- SearchSecurity: Ransomware (read October 6, 2026)
- ZDNet: Free decrypter released for STOP ransomware, today's most popular ransomware strain (read October 6, 2026)
- Emsisoft: Ransomware statistics for 2019: Q2 to Q3 report (read October 6, 2026)
- Lesvirus: Lesvirus (read October 6, 2026)
- CISA: StopRansomware (read October 6, 2026)