CryptoDefense ransomware: what it is and how to remove it
CryptoDefense (also known as HOW_DECRYPT.txt) is a very dangerous cyber infection, which belongs to the ransomware category. The most important thing about this virus is encrypting all your text files, videos, office documents, and similar data.
Facts checked October 7, 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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CryptoDefense ransomware: summary
| Detection names | No Microsoft detection name is known |
|---|---|
| Ransom note | HOW_DECRYPT.txt; the text is quoted in full below |
| Contact | Not recorded in our earlier report |
| Encrypted file extension | Not recorded in our earlier report |
| Decryptor | No free decryptor is known for this variant; check No More Ransom (nomoreransom.org) for updates |
| Distribution | Not recorded in the old report |
| 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 8 more facts
| Damage | Not recorded in the old report |
|---|---|
| Name | CryptoDefense |
| Type | File-encrypting ransomware |
| Symptoms | A ransom note left in folders |
| Evidence | One write-up by a security site; details still limited |
| Free decryptor | No free decryptor is known (checked 7 October 2026) |
| First seen | 9 March 2021 |
| Facts checked | 7 October 2026 |
What to search your PC and browser for
- Note file:
HOW_DECRYPT.txt
The CryptoDefense ransomware note
All files including videos, photos and documents on your computer are encrypted by CryptoDefense Software.
Encryption was produced using a unique public key RSA-2048 generated for this computer. To decrypt files you need to obtain the private key.
The single copy of the private key, which will allow you to decrypt the files, located on a secret server on the Internet;
the server will destroy the key after a month. After that, nobody and never will be able to restore files.
How to remove CryptoDefense 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 CryptoDefense 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
CryptoDefense encrypts everything it can reach, including drives and shares you connect later. Cut the network first: cable out, or Wi-Fi off from the taskbar.
Then unplug every USB stick and backup disk and pause cloud sync, so the encrypted versions do not replace your online copies. Do not reconnect any of them until the ransomware is removed from the Windows 11 or Windows 10 PC.
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 identify the family
Find the ransom note, usually a
.txt,.htmlor .hta file in every folder or on the desktop, and copy it with one or two encrypted files to a USB stick.From another device, upload them to ID Ransomware or No More Ransom's Crypto Sheriff, which name the family from the note and the file extension. Write down the contact address and your personal ID from the note for the report.
Warning: Never contact the attackers from the infected Windows 11 or Windows 10 PC.
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
For CryptoDefense, no free decryptor is known (checked 7 October 2026). Search the family name in the No More Ransom decryption tools list and in the free decryptors of Emsisoft, Avast and Kaspersky, because new tools appear years after an attack.
Important: Keep the encrypted files even if nothing works today, and do not pay before every free option is ruled out: payment does not guarantee a working key.
Decryptors run on Windows 11 and Windows 10, but only after the ransomware itself is removed.
Full procedure with screenshots: Ransomware: first steps, finding a decryptor and recovering files
Step 4: Remove the ransomware before you restore or decrypt
Restoring or decrypting files while CryptoDefense still runs lets it encrypt them again. Run a Full scan in Windows Security > Virus & threat protection > Scan options, then the Microsoft Defender Antivirus (offline scan).
If the ransomware blocks Windows Security, start Safe Mode with Networking and scan from there. Some families install a password stealer as well, so let both scans finish on Windows 11 or 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
Open Command Prompt as administrator and run
vssadmin list shadows. If it lists copies dated before the attack, right-click a folder with encrypted files in File Explorer, choose Properties > Previous Versions, and open or restore a version from before that date.ShadowExplorer, a free tool, shows the same copies when the tab is empty or hidden. Most current families delete shadow copies, so an empty list is normal, but the check takes two minutes on Windows 11 or Windows 10.
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
Restore from an external backup, File History or OneDrive's version history, choosing a date before the attack. Connect the backup drive only after the scans are clean, or the ransomware encrypts it too.
If there is no backup, file recovery software can sometimes find the deleted originals, because some ransomware writes an encrypted copy and deletes the original file.
Stop writing to the drive and try recovery on Windows 11 or Windows 10 before new files overwrite the space.
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 Mar 2021 · not reviewed since
CryptoDefense - malware that prevents access to personal files until ransom is paid
CryptoDefense (also known as HOW_DECRYPT.txt) is a very dangerous cyber infection, which belongs to the ransomware category.
The most important thing about this virus is encrypting all your text files, videos, office documents, and similar data. As a result, none of the files can be opened until a unique key is provided by cybercriminals.
Of course, malware authors are unwilling to give it for free and ask for a ransom that needs to be paid in bitcoin cryptocurrency. Users allegedly then would receive a personal code that can enter into a pop-up window and decrypt all files automatically.
According to experts, CryptoDefense is still incapable of affecting Macs, but it can easily attack all Windows versions, such as:
Similar to ransomware that was discovered before, this variant displays a huge alert after taking over its target PC system. This warning claims that all files were encrypted by CryptoDefense Software and says that the victim needs to obtain the private key to decrypt them.
Of course, this service is not for free – scammers ask paying $500 in bitcoins. If you fail to pay, they promise that after four days the ransom will be doubled. Unfortunately, there is still no method to decrypt files that were encrypted by the CryptoDefense virus. Therefore, you should always make sure that you have working backups prepared - they should be stored on a separate medium.
As soon as the virus enters the system, it encrypts data files and starts showing this notification:
CryptoDefense instructs people how they can pay the ransom and purchase a tool for decryption. For that, they need to visit specific site, enter their unique key and then reveal how much bitcoins they need to pay. As we have said, delaying this may increase the amount of ransom and instead of $500 you may have to pay $1,000 in bitcoins.
Instead, remove ransomware with or another tool, and then use alternative methods for data recovery we provide below.
- Windows XP
- Windows Vista
- Windows 7
- Windows 10, etc.
From our report of Mar 2021 · not reviewed since
Ransomware distribution and prevention methods
Ransomware is possibly on the most devastating computer infections in the wild.
It became one of the most lucrative illegal businesses around, and there are new strains emerging every day. One of the most damaging ransomware features is that the elimination of malware would not restore files to their previous states. The encrypted data requires a unique key that is in the possession of cybercriminals behind the attack.
That's why you need to understand how to avoid ransomware. The most important thing in this situation is to ignore all unfamiliar emails that typically report about nonexistent purchases, payments, and similar things that could make people click on the malicious link.
Similarly to CTB Locker, CryptorBit, and CryptoLocker viruses, it may also enter your PC in a bundle with fake Flash and Java updates, so ignore all unexpected alerts offering downloading them for free.
From our report of Mar 2021 · not reviewed since
Delete CryptoDefense ransomware before attempting file recovery
If you need to remove CryptoDefense from your computer, you need to perform a full system scan with powerful anti-malware software, such as . can also be useful when dealing with virus damage to the system files. If the malware is interfering with its functions, you can try accessing Safe Mode with networking, as explained below.
After CryptoDefense removal, you should restore all your files from backups. Unfortunately, most people don't have adequate backups prepared, and end up losing their data after a ransomware attack. Not all hope is lost, however, - we provide a few alternative methods that might help you to recover at least some of your lost files.
Also, you should start thinking about the prevention of such infections. For that, you can use the previously mentioned programs. Besides, don't forget to think about the immunity of your files and backup. For that, you can use:
- USB external hard drives, CDs, DVDs;
- rely on online backups, such as Google Drive, Dropbox, Flickr, and other solutions.
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.
Protect the files you restore
Restore only after the scans are clean and the PC no longer shows ransom notes called HOW_DECRYPT.txt in every folder; otherwise the restored copies can be damaged again.
Then build a backup that survives the next infection:
- one copy in the cloud with version history
- one on an external drive that is disconnected between backups
- the working copy on the PC
Version history matters because a backup that syncs damaged files overwrites the good ones.
How to do this with the tools built into Windows: the 3-2-1 backup rule on Windows.
Do not let government spy on you
The government has many issues in regards to tracking users' data and spying on citizens, so you should take this into consideration and learn more about shady information gathering practices.
Avoid any unwanted government tracking or spying by going totally anonymous on the internet.
You can choose a different location when you go online and access any material you want without particular content restrictions. You can easily enjoy internet connection without any risks of being hacked by using VPN.
Control the information that can be accessed by government any other unwanted party and surf online without being spied on. Even if you are not involved in illegal activities or trust your selection of services, platforms, be suspicious for your own security and take precautionary measures by using the VPN service.
Backup files for the later use, in case of the malware attack
Computer users can suffer from data losses due to cyber infections or their own faulty doings.
Ransomware can encrypt and hold files hostage, while unforeseen power cuts might cause a loss of important documents. If you have proper up-to-date backups, you can easily recover after such an incident and get back to work. It is also equally important to update backups on a regular basis so that the newest information remains intact - you can set this process to be performed automatically.
When you have the previous version of every important document or project you can avoid frustration and breakdowns. It comes in handy when malware strikes out of nowhere. Use for the data restoration process.
Questions about CryptoDefense ransomware
When will a decryptor for CryptoDefense be released?
Nobody can promise a date. When we last checked, on 7 October 2026, no free decryptor is known. Decryptors usually appear after one of three events:
- police seize the attackers' servers and keys
- the authors leak or publish the master keys
- researchers find a mistake in how the ransomware generates keys
Some families got a tool within weeks, others never. Keep the encrypted files and the note on an external drive, check No More Ransom every few months, and follow news about the CryptoDefense family. A decryptor may need an original file, so keep any unencrypted copies too.
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.
How did CryptoDefense get on my computer?
The way CryptoDefense 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 ransom notes called HOW_DECRYPT.txt in every folder, and check the Downloads folder and Installed apps sorted by date. Keep anything suspicious for your report, but do not run it again.
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.
Did CryptoDefense steal my files or passwords?
We do not know yet. Nothing published so far shows data theft by CryptoDefense, but the only confirmed sign is ransom notes called HOW_DECRYPT.txt in every folder, 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 CryptoDefense 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 HOW_DECRYPT.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. HOW_DECRYPT.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.
Can I get my files back without paying after HOW_DECRYPT.txt appeared?
Sometimes. Free decryptors exist for a number of families, especially older ones or those with flaws in their encryption. Other routes are copies the ransomware missed:
- OneDrive version history
- File History
- a backup drive that was disconnected
- email attachments
- phone photos
Shadow copies are often deleted, but it is worth checking. Identify the family from HOW_DECRYPT.txt first, because that tells you which of these routes is realistic. Keep encrypted files even if nothing works now; decryptors are sometimes released months later.
How do I open my .docx, .jpg and other files locked by CryptoDefense?
You cannot open locked files normally while they stay encrypted, and renaming them will not help. Our earlier report did not record the extension that CryptoDefense adds, so check one locked file name and the ransom note for it.
No free decryptor is known for this variant; check No More Ransom (nomoreransom.org) for updates. Do not rename the files, change the extension or edit them, because that can make recovery harder. Copy the locked files to an external drive before you clean the system, so a decryptor released later still has them.
Will Fortect remove CryptoDefense?
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 CryptoDefense, 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
- CISA: StopRansomware (read October 7, 2026)
- No More Ransom (read October 7, 2026)
- FTC: How to recognize, remove and avoid malware (read October 7, 2026)
- Microsoft Learn: Microsoft Defender Offline (read October 7, 2026)
- Microsoft Learn: How Microsoft names malware (read October 7, 2026)