4k Ransomware

Also Known As: 4k virus
Distribution: Low
Damage level: Severe

4k ransomware removal instructions

What is 4k?

4k is the name of a ransomware-type program designed to blackmail victims by encrypting their data and forcing them to pay a ransom. It was discovered by Jakub Kroustek and is a part of a ransomware family called Dharma. 4k changes each filename by adding the ".4k" extension plus the victim's ID and the email address of the cyber criminals who developed it. For example, "1.jpg" might be renamed to a filename such as "1.jpg.id-1E857D00.[rocosmon@cock.li].4k". It also generates two ransom notes: one in a pop-up window and the other in the "RETURN FILES.txt" file.

The text file states that all of the victim's files are encrypted and can only be recovered by contacting cyber criminals via the rocosmon@cock.li email address. The pop-up window contains more detail. It states that 4k encrypted files with RSA-1024 encryption. To restore/decrypt them, victims are encouraged to contact 4k's developers via the same email address that is provided in the "RETURN FILES.txt" file, however, the pop-up window states that this should be done within seven days after encryption, since, later, decryption keys might be overwritten and victims will then be unable to decrypt their files. The cost of a decryption tool/key is unknown, however, this should be given after 4k's developers are contacted. Most cyber criminals ask to be paid in a cryptocurrency (such as Bitcoins). Cyber criminals who developed this ransomware promise to send a decryption tool/key and instructions on how to use them immediately after payment. They even offer free decryption of one file, which can be sent to them via the email address, before making payment. Even if these people have the correct decryption tool, they should not be trusted. Most ransomware developers do not send any tools that decrypt files. Once they receive payment via a cryptocurrency, they do not reply to victims or send any decryption tools/keys. Therefore, do not contact or pay these cyber criminals and ransomware developers. Unfortunately, there are no tools capable of decrypting 4k encryption free of charge. The only way to recover files is to restore everything from a data backup.

Screenshot of a message encouraging users to pay a ransom to decrypt their compromised data:

4k decrypt instructions

4k shares similarities with many other ransomware-type programs of this type including PLUT, Jack, and DDOS. This malware encrypts files and displays ransom messages encouraging people to purchase tools requited for decryption. Any differences are cost of decryption and cryptography algorithm used to perform the encryption. Note that encryptions caused by ransomware are virtually impossible to decrypt without the involvement of cyber criminals (and the tools only they have). Decryption is possible only in cases when ransomware-type programs are not fully developed, have bugs/flaws, and so on. To avoid data/financial loss, maintain backups and store them on a remote server or unplugged storage device.

How did ransomware infect my computer?

Cyber criminals proliferate malicious programs in various ways - mostly via spam campaigns (emails), software 'cracking' tools, trojans, dubious software download channels and unofficial software updaters. One of the most common ways to trick people into infecting their computers is to send emails that contain malicious attachments. When people open them, they allow the files to download and install malware. Some examples of attachments that cyber criminals send are Microsoft Office documents, executables, PDF documents, archive files such as ZIP, RAR, JavaScript files and so on. Software activation performed using 'cracking' tools can lead to installation of high-risk viruses. Programs of this type are often used to proliferate malware and do not operate as advertised. Trojans can be used to proliferate malware. These programs usually cause chain infections and proliferate other malicious software. Peer-to-peer networks (such as torrents, eMule, and so on), third party downloaders/installers, freeware download websites or file hosting websites can be used to infect computers by presenting malicious files as legitimate. By downloading and opening them, unsuspecting people install computer infections. If used, fake software updaters exploit bugs/flaws of installed software or download and install malicious programs rather than installing updates or fixes.

Threat Summary:
Name 4k virus
Threat Type Ransomware, Crypto Virus, Files locker
Encrypted Files Extension .4k (this ransomware also appends filenames with the victim's unique ID and developer's email address).
Ransom Demanding Message Pop-up window, RETURN FILES.txt text file.
Cyber Criminal Contact rocosmon@cock.li
Detection Names (p.exe) Avast (Win32:Malware-gen), BitDefender (Trojan.Ransom.Crysis.E), ESET-NOD32 (a variant of Win32/Filecoder.Crysis.P), Kaspersky (Trojan-Ransom.Win32.Crusis.to), Full List Of Detections (VirusTotal)
Symptoms Cannot open files stored on your computer, previously functional files now have a different extension (for example, my.docx.locked). A ransom demand message is displayed on your desktop. Cyber criminals demand payment of a ransom (usually in bitcoins) to unlock your files.
Distribution methods Infected email attachments (macros), torrent websites, malicious ads.
Damage All files are encrypted and cannot be opened without paying a ransom. Additional password-stealing trojans and malware infections can be installed together with a ransomware infection.
Malware Removal (Windows)

To eliminate possible malware infections, scan your computer with legitimate antivirus software. Our security researchers recommend using Malwarebytes.
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How to protect yourself from ransomware infections?

Be careful with attachments (or links) presented in irrelevant emails that are received from unknown, dubious addresses. These emails are often presented as official, however, they should not be trusted. The safest way to download software (especially freeware) is using official websites. Tools mentioned above should not be used. The same applies to software updates: it is important to update installed software using tools (or functions) that are provided by official software developers. Unofficial tools might infect computers. If software requires activation, do not use 'cracking' to bypass it. Using these tools is a cyber crime and might lead to download and installation of malware. Use the computer and browse the web only if you have anti-virus or anti-spyware software installed and enabled. If your computer is already infected with 4k, we recommend running a scan with Malwarebytes for Windows to automatically eliminate this ransomware.

Text presented in 4k ransomware text file:

You can send us up to 1 file for free decryption. The total size of files must be less than 1Mb (non archived), and files should not contain valuable information. (databases,backups, large excel sheets, etc.)
When you make sure of decryption possibility transfer the money to our bitcoin wallet. As soon as we receive the money we will send you:
1. Decryption program.
2. Detailed instruction for decryption.
3. And individual keys for decrypting your files.
Do not rename encrypted files.
Do not try to decrypt your data using third party software, it may cause permanent data loss.
Decryption of your files with the help of third parties may cause increased price (they add their fee to our) or you can become a victim of a scam.

Screenshot of 4k text file ("RETURN FILES"):

4k text file

Screenshot of 4k text file:

All your data is encrypted!
for return write to mail:

Screenshot of files encrypted by 4k (".4k" extension):

Files encrypted by 4k

4k ransomware removal:

Instant automatic malware removal: Manual threat removal might be a lengthy and complicated process that requires advanced computer skills. Malwarebytes is a professional automatic malware removal tool that is recommended to get rid of malware. Download it by clicking the button below:
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Quick menu:

Step 1

Windows XP and Windows 7 users: Start your computer in Safe Mode. Click Start, click Shut Down, click Restart, click OK. During your computer start process, press the F8 key on your keyboard multiple times until you see the Windows Advanced Option menu, and then select Safe Mode with Networking from the list.

Safe Mode with Networking

Video showing how to start Windows 7 in "Safe Mode with Networking":

Windows 8 users: Start Windows 8 is Safe Mode with Networking - Go to Windows 8 Start Screen, type Advanced, in the search results select Settings. Click Advanced startup options, in the opened "General PC Settings" window, select Advanced startup. Click the "Restart now" button. Your computer will now restart into the "Advanced Startup options menu". Click the "Troubleshoot" button, and then click the "Advanced options" button. In the advanced option screen, click "Startup settings". Click the "Restart" button. Your PC will restart into the Startup Settings screen. Press F5 to boot in Safe Mode with Networking.

Windows 8 Safe Mode with networking

Video showing how to start Windows 8 in "Safe Mode with Networking":

Windows 10 users: Click the Windows logo and select the Power icon. In the opened menu click "Restart" while holding "Shift" button on your keyboard. In the "choose an option" window click on the "Troubleshoot", next select "Advanced options". In the advanced options menu select "Startup Settings" and click on the "Restart" button. In the following window you should click the "F5" button on your keyboard. This will restart your operating system in safe mode with networking.

windows 10 safe mode with networking

Video showing how to start Windows 10 in "Safe Mode with Networking":

Step 2

Log in to the account infected with the 4k virus. Start your Internet browser and download a legitimate anti-spyware program. Update the anti-spyware software and start a full system scan. Remove all entries detected.

If you cannot start your computer in Safe Mode with Networking, try performing a System Restore.

Video showing how to remove ransomware virus using "Safe Mode with Command Prompt" and "System Restore":

1. During your computer start process, press the F8 key on your keyboard multiple times until the Windows Advanced Options menu appears, and then select Safe Mode with Command Prompt from the list and press ENTER.

Boot your computer in Safe Mode with Command Prompt

2. When Command Prompt mode loads, enter the following line: cd restore and press ENTER.

system restore using command prompt type cd restore

3. Next, type this line: rstrui.exe and press ENTER.

system restore using command prompt rstrui.exe

4. In the opened window, click "Next".

restore system files and settings

5. Select one of the available Restore Points and click "Next" (this will restore your computer system to an earlier time and date, prior to the 4k ransomware virus infiltrating your PC).

select a restore point

6. In the opened window, click "Yes".

run system restore

7. After restoring your computer to a previous date, download and scan your PC with recommended malware removal software to eliminate any remaining 4k ransomware files.

To restore individual files encrypted by this ransomware, try using Windows Previous Versions feature. This method is only effective if the System Restore function was enabled on an infected operating system. Note that some variants of 4k are known to remove Shadow Volume Copies of the files, so this method may not work on all computers.

To restore a file, right-click over it, go into Properties, and select the Previous Versions tab. If the relevant file has a Restore Point, select it and click the "Restore" button.

Restoring files encrypted by CryptoDefense

If you cannot start your computer in Safe Mode with Networking (or with Command Prompt), boot your computer using a rescue disk. Some variants of ransomware disable Safe Mode making its removal complicated. For this step, you require access to another computer.

To regain control of the files encrypted by 4k, you can also try using a program called Shadow Explorer. More information on how to use this program is available here.

shadow explorer screenshot

To protect your computer from file encryption ransomware such as this, use reputable antivirus and anti-spyware programs. As an extra protection method, you can use programs called HitmanPro.Alert and EasySync CryptoMonitor, which artificially implant group policy objects into the registry to block rogue programs such as 4k ransomware.

Note that Windows 10 Fall Creators Update includes a "Controlled Folder Access" feature that blocks ransomware attempts to encrypt your files. By default, this feature automatically protects files stored in the Documents, Pictures, Videos, Music, Favorites as well as Desktop folders.

Controll Folder Access

Windows 10 users should install this update to protect their data from ransomware attacks. Here is more information on how to get this update and add an additional protection layer from ransomware infections.

HitmanPro.Alert CryptoGuard - detects encryption of files and neutralises any attempts without need for user-intervention:

hitmanproalert ransomware prevention application

Malwarebytes Anti-Ransomware Beta uses advanced proactive technology that monitors ransomware activity and terminates it immediately - before reaching users' files:

malwarebytes anti-ransomware

  • The best way to avoid damage from ransomware infections is to maintain regular up-to-date backups. More information on online backup solutions and data recovery software Here.

Other tools known to remove 4k ransomware:

About the author:

Tomas Meskauskas

Tomas Meskauskas - expert security researcher, professional malware analyst.

I am passionate about computer security and technology. I have an experience of over 10 years working in various companies related to computer technical issue solving and Internet security. I have been working as an author and editor for pcrisk.com since 2010. Follow me on Twitter and LinkedIn to stay informed about the latest online security threats. Contact Tomas Meskauskas.

PCrisk security portal is brought by a company RCS LT. Joined forces of security researchers help educate computer users about the latest online security threats. More information about the company RCS LT.

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Malware activity

Global malware activity level today:

Medium threat activity

Increased attack rate of infections detected within the last 24 hours.

QR Code
4k virus QR code
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