Trojan.Encoder.6491: what it is and how to remove it
Trojan.Encoder.6491 virus is a newly released ransomware that has been defeated just after three days since its first emergence. This unsuccessful ransomware example is coded using Go language, and reportedly is distributed in the form of Windows_Security.exe file.
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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Trojan.Encoder.6491: summary
| Detection names | No Microsoft detection name is known |
|---|---|
| Distribution | Not recorded in the old report |
| Damage | Not recorded in the old report |
| Name | Trojan.Encoder.6491 |
| Type | Loader |
| Symptoms | An unknown process in Task Manager |
| 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 4 more facts
| Evidence | One write-up by a security site; details still limited |
|---|---|
| File names | Windows_Security.exe |
| First seen | 13 October 2016 |
| Facts checked | 7 October 2026 |
What Trojan.Encoder.6491 does on an infected PC
From our report of Oct 2016 · not reviewed since
Trojan.Encoder.6491 is the first ransomware variant written in Google's Go programming language
Trojan.Encoder.6491 virus is a newly released ransomware that has been defeated just after three days since its first emergence.
This unsuccessful ransomware example is coded using Go language, and reportedly is distributed in the form of Windows_Security.exe file. If you follow computer security news, you probably know that ransomware authors love to use a new technique to encrypt victim's files quickly and silently - they launch a fake screen that looks like Windows Update screen, and in the meantime, corrupts all files on the system.
Trojan.Encoder.6491 ransomware uses the same technique and locks the files with advanced encryption standard (AES cipher). The virus encrypts files by file extensions they have, and it targets more than 140 different file types. Once it finds target file, encrypts it and appends a .enc file extension to it.
Please do not confuse this virus with TrueCrypter or Crypt0L0cker viruses, which also attach the same extension to encrypted files. However, Trojan.Encoder.6491 malware does not only append new file extension but also distorts the filename by applying the Base64 algorithm. This modification does not allow the victim to identify corrupted files.
After applying all changes to victim's files, the virus displays a ransom note, which contains all information about the data encryption and decryption processes. The victim is asked to pay around 25 USD in Bitcoins, which is 0.052300 BTC. There is also an e-mail provided at the end of the note for those who have any questions - helpmedecrypt@protonmail.com.
However, if your files have been encrypted by Trojan.Encoder.6491 ransomware virus, do not waste your money and better use it for a better purpose, for example, protection of your computer system. We have some good news for you - this virus has some flaws that allows victims to decrypt .enc files.
The decryption tool has not been released publicly yet, but soon it is going to be available to everyone. However, you should try to decrypt data only after removing the virus. To remove Trojan.Encoder.6491 malware, use software or the one you already have. Make sure you update it first to ensure a successful Trojan.Encoder.6491 removal!
From our report of Oct 2016 · not reviewed since
How does this ransomware infect computers?
You can infect your computer with this ransomware by opening random email letters and files attached to them.
Sending tons of malicious email attachments to victims is the primary ransomware distribution method, so before opening an email that is sent by an unknown sender, think twice.
We bet that you do not want to compromise the computer system by accident, so stay away from Spam and Junk sections in your email, but keep in mind that some malicious letters can bypass these email filters and go straight to the Inbox.
Ransomware can infect unprotected computers as soon as the victim clicks on a malevolent ads or visits an infectious website that contains an exploit kit. Avoid such dangers by installing a trustworthy anti-malware software.
How to check the PC for Trojan.Encoder.6491
- File:
Windows_Security.exe
How to remove Trojan.Encoder.6491
A loader's job is to install other malware, so treat the PC as infected with more than one program until the scans are clean.
Step 1: Check where Windows_Security.exe runs from and stop it
Windows_Security.exeis the part you can see, and its location tells you whether it belongs there. Right-click it on the Processes page of Task Manager and choose Open file location, then right-click the file > Properties > Digital Signatures to see who signed it.An unsigned file, or one in a user folder such as
%AppData%, is the one to remove: end the task, then delete the file.Note the folder name, because the same folder usually holds its other files. This is the same in Windows 11 and Windows 10.
Full procedure with screenshots: Close a frozen app (Task Manager, Force Quit) On uGetFix
Step 2: Delete scheduled tasks that bring it back
Open Task Scheduler from the Start menu and click Task Scheduler Library. Select each task you do not recognise and read the Actions tab:
- a task that starts a file in
%AppData%or%Temp% - runs
powershellwith a long encoded line - opens a web address belongs to Trojan.Encoder.6491 or a similar program
Right-click such a task and choose Delete, and check the subfolders too. Leave tasks from Microsoft, your PC's maker and programs you use. Task Scheduler is the same in Windows 11 and Windows 10.
Windows 11: Task Scheduler Library, the task selected, the Actions tab shows the file it runs. Full procedure with screenshots: Remove what malware leaves behind in Windows
- a task that starts a file in
Step 3: Remove it from startup
Whatever Trojan.Encoder.6491 installed usually starts with Windows. Open Task Manager with Ctrl + Shift + Esc, go to Startup apps in Windows 11 or the Startup tab in Windows 10, and disable what you do not know, starting with entries that have an empty Publisher column.
Open file location on the right-click menu shows the file, which helps you decide and tells you what to delete later. Disabling is safe: if something you need stops working, switch it back on.
Full procedure with screenshots: Stop apps from opening at startup On uGetFix
Step 4: Delete the folders left behind
What the uninstaller leaves behind is usually in the user folders. Open File Explorer, switch on View > Show > Hidden items (in Windows 10 View > Hidden items), and go through
%LocalAppData%,%AppData%, %ProgramData% and the two Program Files folders.Sort by Date modified and delete folders that appeared together with the problem and belong to no program you use. Folders with random names that hold
.exe,.dll, .js or .ps1 files are the strongest sign.Full procedure with screenshots: Remove what malware leaves behind in Windows
Step 5: Scan the PC, then run the offline scan
Open Windows Security > Virus & threat protection > Scan options, run a Full scan and remove everything it finds. Then select Microsoft Defender Antivirus (offline scan) and click Scan now: the PC restarts and scans before Windows loads, which finds files that hide while Windows runs.
Save your work first, because the offline scan takes about 15 minutes. Both scans are built into Windows 11 and Windows 10, and a second scanner from another vendor is a useful extra opinion.
Windows 11: Windows Security > Virus & threat protection > Scan options. Full procedure with screenshots: Run a Microsoft Defender Offline scan
Step 6: Change passwords from another device and sign out other sessions
Assume that the passwords saved in this PC's browsers, and the accounts that were open in them, are known to the attacker. From a phone or a clean computer, change the e-mail password first, then banking, shopping, social and gaming accounts.
Use each service's option to sign out of all other sessions, because stolen cookies keep a session open even after a password change. Turn on two-step verification on each account. Wait with the infected Windows 11 or Windows 10 PC until the scans are clean.
Full procedure with screenshots: Turn on two-step verification / secure a hacked account
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 Oct 2016 · not reviewed since
Remove Trojan.Encoder.6491 virus and decrypt .enc files
Please use Trojan.Encoder.6491 removal instructions provided below to prepare your PC before you run an anti-malware software.
This way, the virus will be deactivated, and anti-virus software will be able to do its job. You can leave some malicious files on the system and make it vulnerable to further malware attacks!
If you want, you can try this data recovery method to restore files encrypted by Trojan.Encoder.6491 ransomware:
Trojan.Encoder.6491 decryption tool
At the moment, Trojan.Encoder.6491 decryption tool is available only for people who purchase a certain computer protection software - the anti-virus company does not allow victims to use this tool for users of other anti-virus programs. However, considering that this ransomware is full of flaws, other malware researchers should release free decryption tools shortly. Be patient! We will update the article as soon as such tools appear.
After removal: passwords, accounts and prevention
Accounts come next
Because the PC showed an unfamiliar process called Windows_Security.exe in Task Manager, a sign of a program that could read browser data, the clean-up is only half of the work.
The other half happens in your online accounts.
Change passwords from a clean device, beginning with e-mail; sign out of all sessions; check forwarding rules and recovery phone numbers; and turn on two-step verification with an authenticator app or a passkey. Ask your bank to replace cards saved in the browser.
Why the order matters and what to check in each account: secure your accounts after malware.
Access your website securely from any location
When you work on the domain, site, blog, or different project that requires constant management, content creation, or coding, you may need to connect to the server and content management service more often. The best solution for creating a tighter network could be a dedicated/fixed IP address.
If you make your IP address static and set to your device, you can connect to the CMS from any location and do not create any additional issues for the server or network manager that needs to monitor connections and activities. VPN software providers like can help you with such settings and offer the option to control the online reputation and manage projects easily from any part of the world.
Recover files after data-affecting malware attacks
While much of the data can be accidentally deleted due to various reasons, malware is one of the main culprits that can cause loss of pictures, documents, videos, and other important files.
More serious malware infections lead to significant data loss when your documents, system files, and images get encrypted. In particular, ransomware is is a type of malware that focuses on such functions, so your files become useless without an ability to access them.
Even though there is little to no possibility to recover after file-locking threats, some applications have features for data recovery in the system. In some cases, can also help to recover at least some portion of your data after data-locking virus infection or general cyber infection.
Questions about Trojan.Encoder.6491
Is Windows_Security.exe safe?
It depends on where the file is and who signed it, not on the name. Open Task Manager, go to the Details tab, right-click Windows_Security.exe and choose Open file location. A file inside Program Files or System32 with a valid digital signature from a known company is usually part of a legitimate program.
A file in AppData, Temp or ProgramData with no signature, especially one that restarts itself after you end it, is suspicious. If you cannot tie the process to anything you installed, uninstall recent unfamiliar programs and run a Microsoft Defender Offline scan.
Windows_Security.exe keeps coming back. What should I do?
A process that returns after you end it has a restart mechanism, and that is a reason to treat Windows_Security.exe as unwanted. Check Settings > Apps > Startup, Task Scheduler and the Services list for entries pointing to its folder, and disable them.
Look in Installed apps for anything added the same day and uninstall it. Then delete the folder and run a Microsoft Defender Offline scan, which works before Windows starts and can remove files that are locked or hidden while the system is running.
Can I just delete Windows_Security.exe?
Deleting Windows_Security.exe by hand rarely removes Trojan.Encoder.6491. While the trojan runs, Windows may refuse to delete the file, and if you succeed, a scheduled task, a service or a second copy may bring it back at the next restart.
The file can also be only one part of the infection: loaders and remote access tools often install other programs. Use the Microsoft Defender offline scan, which removes the file together with its startup entries before Windows loads, and then check startup items and scheduled tasks as described in the plan.
Why can't I find Trojan.Encoder.6491 in antivirus databases?
Because it is new or because it is listed under a different name. Antivirus companies name threats after the family they belong to, and a program that appears as Trojan.Encoder.6491 on your PC may carry a generic or unrelated label in their databases.
Many new samples are first detected only by behaviour, without a family name. What you saw, an unfamiliar process called Windows_Security.exe in Task Manager, is enough to act on:
- end the program
- remove its startup entry
- run a Microsoft Defender offline scan
- secure your accounts
A detection name from a scan is worth noting for later.
Should I reset my PC because of Trojan.Encoder.6491?
Only if the signs point to deeper access. Reset when you see an unfamiliar process called Windows_Security.exe in Task Manager again after removal, when Windows Security cannot start or update, when remote access tools you did not install keep appearing, or when you simply cannot trust the PC any more.
Otherwise, the plan in this guide plus an offline scan is enough. If you do reset, choose Remove everything and Cloud download for a fresh copy of Windows, restore only documents and photos, and reinstall programs from their official sites. Change important passwords from the clean system afterwards.
What are the signs of a trojan infection?
Most trojans try to leave no visible signs, so look for side effects. Common ones:
- Windows Security turned off or unable to update
- new entries in Startup apps or Task Scheduler
- programs in Installed apps you did not install
- browser settings that changed by themselves
- unusual network activity while the PC is idle
- password-reset or login-alert e-mails you did not trigger
None of these proves an infection on its own. Together with an antivirus alert naming Trojan.Encoder.6491, they are a strong reason to follow the full plan.
Can a normal remote support program be a backdoor?
Yes. Tools such as AnyDesk, TeamViewer and ScreenConnect are legitimate, but whoever controls the account behind them controls the PC. Scammers install them during fake support calls, and some trojan campaigns install them silently because antivirus programs do not flag a genuine, signed product.
If you find one you did not set up, uninstall it, check Startup apps for related entries and change passwords from another device. If money or accounts were involved, call your bank and report the incident.
Is a trojan infection worth reporting to the police?
If there was harm, yes. Unauthorised payments, accounts used for fraud, blackmail or a remote session during a scam call all belong in a report, and banks often ask for its reference number before they refund anything.
If antivirus caught Trojan.Encoder.6491 before it ran and nothing was misused, there is nothing to report. Keep the evidence anyway:
- protection history
- the original download
- the dates
Businesses may also have to notify a data protection authority if personal data could have been accessed.
Can Trojan.Encoder.6491 spread to other devices on my network?
Most trojans aimed at home users stay on the PC they infected, but an attacker with remote access can look at the network, open shared folders and try passwords on other devices. Loaders sometimes deliver worms or ransomware that do spread.
Disconnect the PC while cleaning, run a full scan on other Windows PCs, change the router's admin password and the Wi-Fi password if they were saved on the infected PC, and update the router's firmware. If other PCs show the same detection, treat them as infected too.
Will Fortect remove Trojan.Encoder.6491?
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 Trojan.Encoder.6491, 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
- 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)