CRIMSON Ransomware Virus: How to Remove It and Recover .crimson Files Safely

Your documents suddenly end in .crimson, refuse to open, and a red full-screen message demands contact with the attackers. This is not a Windows error. CRIMSON ransomware has encrypted the computer’s data.

Disconnect the affected PC immediately. Avoid unnecessary restarts, and do not contact or pay the attackers before preserving evidence, checking backups and looking for a legitimate recovery option.

Overview

CRIMSON is Windows ransomware that encrypts files and holds them hostage. On an infected computer, a file such as 1.jpg becomes 1.jpg.crimson, while documents, archives, databases and other personal data become unreadable.

After encryption, CRIMSON displays a full-screen ransom message. It claims that documents, databases, photos and backups were protected with RSA-4096 encryption and tells the victim to contact crimson@onionmail.org. The screen also shows a Machine ID and an RSA public key tied to the infected system.

The attackers warn victims not to attempt recovery and not to shut down or restart the computer. Those commands are designed to keep the criminals in control of the situation. The urgent priority is to isolate the PC from networks and storage devices so the ransomware cannot reach additional data.

There is currently no confirmed free decryptor for CRIMSON. That does not mean paying is the answer. A ransom payment buys only a promise from criminals, with no guarantee that a working key will arrive or that stolen information will be deleted.

Removing the ransomware stops the active threat but does not automatically decrypt files that already carry the .crimson extension. Recovery is a separate process involving clean offline backups, cloud version history, unaffected copies or a future decryptor developed after researchers identify a weakness.

CRIMSON should be treated as a full security incident, not just a file problem. Ransomware is often delivered alongside password stealers, downloaders or remote-access malware, so important accounts used on the infected PC may also need to be secured from a clean device.

What CRIMSON Ransomware Changes

• File extensions: encrypted files receive the .crimson suffix.
• File access: photos, documents, databases and backups no longer open normally.
• Ransom message: a full-screen CRIMSON warning replaces the normal desktop view.
• Victim identity: the note displays a unique Machine ID and public key.
• Contact method: victims are told to email crimson@onionmail.org.
• Recovery pressure: the note warns against independent recovery and restarting.

How the CRIMSON Ransomware Attack Works

Step 1: A malicious file reaches the computer

The exact delivery route can vary. Common ransomware lures include fake invoices, shipping alerts, cracked software, unofficial activators, malicious advertisements, torrents and compromised downloads.

Step 2: The payload executes

An attachment, script or executable runs under the victim’s Windows account. The malware may first establish persistence, weaken security tools or download additional components.

Step 3: Local and connected files are discovered

The ransomware searches the PC and any accessible drives for valuable file types. Connected USB drives, mapped network shares and synchronized folders may also be exposed if they are writable.

Step 4: Files are encrypted and renamed

CRIMSON transforms the contents of targeted files, then appends .crimson. Renaming a file back to its original extension does not reverse the encryption.

Step 5: Recovery options may be targeted

Ransomware families frequently delete shadow copies or interfere with local backups. A backup permanently connected to the infected PC can be encrypted along with the original data.

Step 6: The full-screen demand appears

The ransom screen announces the attack and pushes the victim toward private contact. Machine-specific identifiers allow the criminals to track negotiations and issue different demands.

What to Do Immediately After Finding .crimson Files

• Disconnect Ethernet. Unplug the network cable rather than browsing for help on the infected PC.
• Disable Wi-Fi and Bluetooth. Stop communication with other devices and possible command servers.
• Disconnect external drives. Remove USB storage only after current file activity has stopped.
• Do not delete encrypted files. They may become recoverable if a decryptor is released later.
• Photograph the ransom screen. Preserve the Machine ID, contact address and visible details without communicating with the attackers.
• Tell your IT team. Business networks need immediate containment beyond a single workstation.

Should You Pay the CRIMSON Ransom?

Paying is not a reliable recovery method. The attackers may take the money, demand more, send a broken tool or disappear. Payment also confirms that the victim is willing to negotiate and funds further attacks.

Before considering any irreversible decision, preserve the encrypted data and obtain help from a reputable incident-response or data-recovery professional. Businesses may also have legal, insurance and breach-notification obligations.

How to Remove CRIMSON Ransomware

Step 1: Preserve the encrypted data

If possible, create a sector-level image or a separate copy of encrypted files before cleanup. Do not overwrite the only available copies while testing recovery tools.

Step 2: Identify the infection

The .crimson extension and CRIMSON full-screen note are the main indicators. Save a copy of the ransom message and one small encrypted file for future identification without uploading private documents publicly.

Step 3: Scan and clean the Windows computer

Use the complete MalwareTips Windows removal sequence below. Follow every step because one detection may be only part of the infection chain.

• STEP 1: Uninstall malicious programs from Windows
• STEP 2: Reset browsers back to default settings
• STEP 3: Use Rkill to terminate suspicious programs
• STEP 4: Use Malwarebytes to remove Trojans and unwanted programs
• STEP 5: Use HitmanPro to remove rootkits and other malware
• STEP 6: Use AdwCleaner to remove malicious browser policies and adware
• STEP 7: Perform a final check with ESET Online Scanner

STEP 1: Uninstall malicious programs from Windows

First, we’ll manually check your computer for unknown or malicious programs. Adware and browser hijackers often have a working uninstall entry — removing them this way takes care of the easy part before we run the scanners.

With the malicious programs removed, you’re ready for the next step in this guide.

STEP 2: Reset browsers back to default settings

In this step, we will remove spam notifications,  malicious extensions, and change to default any settings that might have been changed by malware.
Please note that a Chrome or Edge reset turns off all your extensions, and a Firefox refresh removes them. Your bookmarks and favorites stay intact. For each browser that you have installed on your computer, please click on the browsers tab below and follow the displayed steps to reset that browser.

STEP 3: Use Rkill to terminate suspicious programs

Next, we’ll download and run Rkill to stop any suspicious processes running in the background. This prevents the malware from interfering with the removal tools in the following steps.

RKill is a program that was developed at BleepingComputer.com that attempts to terminate known malware processes so that your normal security software can then run and clean your computer of infections. When RKill runs it will kill malware processes and then removes incorrect executable associations and fixes policies that stop us from using certain tools.

1. Download Rkill.

   You can download RKill to your computer from the below link. When at the download page, click on the Download Now button labeled iExplore.exe. We are downloading a renamed version of Rkill (iExplore.exe) because some malware will not allow processes to run unless they have a certain filename.

   

   RKillStops malware processes so other tools can run

   Download RKillOpens the BleepingComputer download page in a new tab.

2. Run RKill.

   After downloading, double-click the iExplore.exe icon to kill malicious processes. In most cases, downloaded files are saved to the Downloads folder.
   The program may take some time to search for and end various malware programs.

   

   When it is finished, the black window will close automatically and a log file will open. Do not restart your computer. Proceed to the next step in this guide.

STEP 4: Use Malwarebytes to remove Trojans and unwanted programs

Now we’ll install Malwarebytes and run a full scan to detect and remove infections, adware, and potentially unwanted programs from your computer.

Malwarebytes is one of the most popular and trusted anti-malware tools for Windows — and it’s completely free for removing infections. It catches threats that many antivirus programs miss, including adware, browser hijackers, and trojans. Follow the steps below to scan your PC and remove what Malwarebytes finds.

1. Download Malwarebytes

   Click the button below to download the latest version of Malwarebytes for Windows from the official source. The free version is all you need — it will scan your computer and remove adware, browser hijackers, and other malicious software at no cost.

   

   Malwarebytes Free for WindowsScans and removes malware at no cost

   Download MalwarebytesOfficial installer for Windows 11 and 10. Your download starts right away.Want real-time protection? See Malwarebytes Premium

2. Install Malwarebytes

   When the download finishes, open your Downloads folder and double-click the MBSetup file. If Windows shows a User Account Control pop-up, click “Yes” to allow the installation.

   

3. Follow the On-Screen Prompts to Install Malwarebytes

   The setup wizard will walk you through a few quick screens:

   • Choose where you’re installing the program — “Personal Computer” or “Work Computer” — then click Next.

     

   • Malwarebytes will now install on your device. This usually takes under a minute.

     

   • When installation is complete, the “Welcome to Malwarebytes” screen will open automatically.

     

   • On the final screen, click Open Malwarebytes to launch the program.

     

4. Optional: Check for rootkits with a Custom Scan

   You don’t need to change any settings for a normal scan. The standard Threat Scan in the next step is enough for most problems, so you can go straight to it.

   If you also want to check for rootkits, use a Custom Scan. In current versions of Malwarebytes, rootkit scanning is only available there:

   1. On the Scanner tile, click the three-dot menu and select Advanced Scan.
   2. Choose Custom Scan. In its options, check Scan for rootkits.
   3. Select your system drive (usually C:\) as the location to scan, then start the scan. It takes longer than a Threat Scan.
   4. When it finishes, review and quarantine the results as described in the steps below.

   Rootkit scanning isn’t available on Windows devices with ARM processors.

5. Start the Scan

   Click the blue Scan button. Malwarebytes will automatically update its virus database and start checking your computer for malware.

   

6. Wait for the Scan to Finish

   The scan checks your entire system for browser hijackers and other malicious programs, so it can take 5 to 20 minutes depending on your computer. Feel free to do something else — just check back occasionally to see the progress.

   

7. Quarantine the Detected Threats

   When the scan is done, you’ll see a list of everything Malwarebytes found — malware, adware, and potentially unwanted programs. Click the “Quarantine” button to remove all of them at once.

   

   Malwarebytes will now remove the malicious files and registry entries and move them safely into quarantine.

   

8. Restart Your Computer

   Some threats can only be fully removed after a reboot. If Malwarebytes asks you to restart, click Yes. Once you’re logged back in, Malwarebytes has finished removing the threats it found.

   

STEP 5: Use HitmanPro to remove rootkits and other malware

Next, we’ll run a second-opinion scan with HitmanPro to catch Trojans, rootkits, and other malicious programs that may have survived the previous step.

HitmanPro is a second-opinion scanner — it’s designed to catch what your main antivirus might have missed. Instead of relying on a single detection engine, it checks the behavior of files in the locations where malware usually hides. Anything suspicious is checked online, where it’s analyzed by several antivirus engines in HitmanPro’s Scan Cloud.

Good news: scanning is completely free, with no limits. You only need a license when it’s time to remove what was found — and even then, you can activate a free one-time 30-day trial to remove what it finds at no cost. The trial works once per computer. After that, removal needs a paid license, and the purchase screen shows the current price.

1. Download HitmanPro

   Click the button below to download HitmanPro. Remember — the scan is free, so you have nothing to lose by checking your PC.

   

   HitmanProSecond-opinion malware scanner from Sophos

   Download HitmanProFree scan. Removing threats needs the free 30-day trial. Opens the official HitmanPro page in a new tab.

2. Install HitmanPro

   When the download finishes, open your Downloads folder and double-click the file “hitmanpro_x64.exe”. (On 32-bit Windows 10, the file is named “hitmanpro.exe”.)

   

   If a User Account Control pop-up asks whether HitmanPro can make changes to your device, click “Yes” to continue.

   

3. Follow the On-Screen Prompts

   On the HitmanPro start screen, click “Next” to begin the system scan. No lengthy setup required — it goes straight to work.

   

   

4. Wait for the Scan to Finish

   HitmanPro will now check your computer for malicious programs. This usually takes just a few minutes thanks to its cloud-based scanning.
   

5. Review the Results and Click “Next”

   When the scan is done, HitmanPro will show you everything it found. Click “Next” to remove the detected threats.

   

6. Click “Activate Free License”

   To remove the malicious files, click the “Activate free license” button. This starts your free 30-day trial — no payment details needed — and unlocks the full cleanup.
   

   When the removal is complete, HitmanPro will show a summary of everything it cleaned. Click Next, then click Reboot if prompted. If there’s no reboot prompt, click Close. Then check whether the problems you noticed have stopped. If they come back, save the HitmanPro log and ask for help in our forum.

STEP 6: Use AdwCleaner to remove malicious browser policies and adware

We’ll now use AdwCleaner to remove malicious browser policies and unwanted browser extensions — the leftovers that keep hijacking your browser settings even after the malware itself is gone.

AdwCleaner is a free on-demand scanner that specializes in adware, browser hijackers, and unwanted toolbars — the exact threats that mainstream antivirus programs often miss. It also includes tools that repair the damage malware leaves behind, like hijacked browser settings and malicious policies. It’s a quick scan that’s well worth running.

1. Download AdwCleaner

   Click the button below to download AdwCleaner — it’s free, portable, and requires no installation.

   

   Malwarebytes AdwCleanerRemoves adware and unwanted programs at no cost

   Download AdwCleanerOpens the official download page in a new tab.

2. Run AdwCleaner

   Open your Downloads folder and double-click the file named “adwcleaner.exe“. There’s no installation — the program starts right away.
   

   If Windows asks whether you want to allow AdwCleaner to run, click “Yes“. When the license agreement appears, click I agree to continue.

   

3. Leave “Reset Chrome policies” off unless you need it

   AdwCleaner can reset Chrome policies, the settings that malware sometimes uses to lock your browser so you can’t change it back. This option removes every Chrome policy, including legitimate ones set by an employer, a school, or parental-control software, so leave it off for a normal scan.

   AdwCleaner applies this option only if you run Basic Repair at the end of the cleanup. Malwarebytes advises running Basic Repair only when a support agent asks you to, and it also runs every other repair action that is turned on in the same list. If this is your own personal PC and chrome://policy in Chrome lists policies you didn’t set, ask for help in our forum instead. On a work or school computer, ask the IT administrator.

4. Start the Scan

   Click “Dashboard” on the left side of the window, then click the “Scan Now” button.

   

5. Wait for the Scan to Finish

   AdwCleaner will now check your computer for adware and other malware. This usually takes only a few minutes — it’s one of the fastest scanners around.

   

6. Quarantine the Detected Threats

   When the scan finishes, AdwCleaner lists everything it found. Review the list and uncheck any program you installed on purpose and want to keep, then click Next. If AdwCleaner also found preinstalled software, it shows that list next. Review it the same way, then click “Quarantine“. Older versions show the Quarantine button on the first list, as in the image below.

   

7. Click “Continue” to Finish the Cleanup

   Save any open work first — AdwCleaner needs to close your open programs before it can clean. When you’re ready, click the “Continue” button.
   

   AdwCleaner will now move the selected items to quarantine. If it asks you to restart your PC, allow it. When you’re back in Windows, AdwCleaner may offer a Basic Repair. Click Skip Basic Repair. Malwarebytes recommends running Basic Repair only when a support agent asks you to. Then check whether the problems you noticed have stopped.

STEP 7: Perform a final check with ESET Online Scanner

Finally, we’ll run ESET Online Scanner as a last check for anything the earlier scans missed. A clean result is a good sign, but no scanner can guarantee that a computer is malware-free.

ESET Online Scanner is a free second-opinion scanner that performs a deep, full-system check for viruses, trojans, rootkits, and other malware. We use it as the final step because it’s thorough and can catch threats the earlier scans missed. A clean result is a good sign, but no scanner can guarantee that a computer is malware-free.

1. Download ESET Online Scanner

   Click the button below to download ESET Online Scanner.

   

   ESET Online ScannerFree one-time malware scan from ESET

   Download ESET Online ScannerOpens the official download page in a new tab.

2. Run the Installer

   When the download finishes, open your Downloads folder and double-click “esetonlinescanner.exe“.
   

3. Install ESET Online Scanner

   On the start screen, select your language from the drop-down menu and click Get started.

   

   On the Terms of use screen, click Accept.
   

   Choose your preferences for the Customer Experience Improvement Program and the Detection feedback system (either choice is fine), then click Continue.
   

4. Start a Full Scan

   Click Full Scan — this checks your entire computer, not just the common hiding spots.

   

   Select Enable for Detection of Potentially Unwanted Applications — this lets ESET catch adware and bundled junk programs, not just viruses. Then click Start scan.

   

5. Wait for the Scan to Finish

   ESET will now check every file on your computer. Because it’s a full scan, this can take a while — often an hour or more, depending on how much data you have. Leave it running in the background and check on it from time to time.

   

6. Review the Results

   When the scan completes, the Found and resolved detections screen appears. Detected threats are usually cleaned and quarantined automatically. Click View detailed results to see exactly what was removed, and ask for help in our forum if any item could not be cleaned.
   

   If ESET found nothing, restart your computer and check whether the problems you noticed have stopped. If they continue, ask for help in our forum.

Step 4: Change exposed credentials

From a clean device, reset passwords for email, banking, cloud storage, work accounts and password managers used on the infected PC. Revoke active sessions and enable multi-factor authentication.

Step 5: Rebuild high-risk systems when necessary

For business computers or devices that handled sensitive information, a clean Windows reinstall may provide more confidence than attempting to repair an unknown compromise. Restore only after the environment is secure.

How to Recover .crimson Files

Restore from an offline backup

The safest recovery method is a backup created before the attack and disconnected from the computer during infection. Scan the rebuilt system before attaching the backup drive.

Check cloud version history

Some cloud services keep earlier versions or deleted-file history. Access the account from a clean device, review the incident date and restore a pre-encryption version where available.

Preserve files for a future decryptor

Keep encrypted copies even if no free tool works today. Researchers may later find a cryptographic flaw, recover keys or seize attacker infrastructure.

Treat random decryptor websites as dangerous

Do not upload sensitive files or pay unknown services that promise instant CRIMSON recovery. Fake decryptors can steal data, demand additional fees or install more malware.

How to Prevent Another Ransomware Attack

• Keep at least one backup offline or otherwise inaccessible from the everyday Windows account.
• Use versioned cloud backups rather than simple folder synchronization alone.
• Patch Windows, browsers, Office and internet-facing software promptly.
• Block Office macros and script execution where they are not required.
• Do not install cracks, pirated software or unofficial update tools.
• Verify unexpected invoices, delivery notices and account alerts through a separate channel.
• Use a standard Windows account for daily work and restrict administrator privileges.
• Test backup restoration regularly instead of assuming the copies work.

Frequently Asked Questions

Can I open a .crimson file by renaming it?

No. The added extension is only a label. The file contents are encrypted, so removing the suffix does not restore the original data.

Is there a free CRIMSON decryptor?

No confirmed free decryptor is currently available. Preserve encrypted files because that situation can change after further analysis.

Will antivirus restore my encrypted files?

Security software can remove the ransomware and related malware, but it cannot usually undo strong encryption. File restoration must come from backups, version history or a legitimate decryptor.

Can CRIMSON spread to network drives?

Any drive or share writable by the infected account may be at risk. Disconnect the computer quickly and have administrators review shared storage for changes.

The Bottom Line

CRIMSON ransomware is a confirmed file-encrypting threat, and the .crimson extension means the affected data has already been altered. Isolate the PC, preserve the encrypted files, remove the malware and recover only from trusted copies. Do not let a full-screen demand rush you into paying criminals for a promise.