How to remove CU ransomware and prevent further file encryption

Also Known As: CU virus
Distribution: Low
Damage level: Severe

CU ransomware removal instructions

What is CU?

CU is the name of malware belonging to the Crysis/Dharma ransomware family. Systems infected with this program have data encrypted and users receive ransom demands for file decryption. When CU ransomware encrypts, all files are renamed according to the following pattern: original filename; unique ID assigned to the victims; cyber criminals' email address, and; the ".CU" extension. For example, a file like "1.jpg" would appear as something similar to "1.jpg.id-1E857D00.[cyberunion@tuta.io].CU". After this process is finished, a text file ("FILES ENCRYPTED.txt") is created on the desktop and a pop-up window is displayed.

The text file informs victims that their data has been compromised and, if they wish to recover it, they must send an email to the addresses provided. The text presented in the pop-up is a more detailed ransom message, which clarifies that the emails users are to send must contain their unique IDs. It further states that, should no response from the criminals arrive within 12 hours, they can use an alternative email address. The message ends with warnings, alerting victims that renaming the encrypted files or attempting decryption with third party decryption tools/software can lead to permanent data loss. Additionally, the pop-up states that seeking the help of third parties can lead to users' falling victims of a scam and increase their financial loss. In most cases of ransomware infections, decryption is impossible without the involvement of cyber criminals responsible. In rare cases, manual decryption might be possible if the malicious program is still in development and/or has bugs/flaws. Whatever the case, you are strongly advised against meeting the ransom demands. Despite paying, victims often receive none of the necessary decryption tools/software. Therefore, their files remain encrypted and they experience significant financial loss. Removing CU ransomware will prevent it from further encryption, however, this will not restore already affected data. The only solution is to recover files from a backup, if one was created prior to the infection and was stored in a different location.

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

CU decrypt instructions (pop-up)

Ransomware is designed to encrypt data and demand payment for decryption tools/software. CryptoPatronumEnCiPhErEdAlphaBetaCrypt and LIVE are a number examples of such programs. The crucial differences between them include cryptographic algorithm they use (symmetric or asymmetric) and ransom size. The sums typically range between three and four digits (in USD). Digital currencies (mainly, cryptocurrencies) are mostly used for these payments, as they are difficult/impossible to trace. To ensure data safety, you are advised to store backups on remote servers and/or unplugged storage devices (ideally, in several separate locations).

How did ransomware infect my computer?

Ransomware and other malware primarily proliferates via trojans, spam campaigns, illegal activation tools ("cracks"), fake updaters and untrusted download channels. Trojans are malicious programs capable of causing chain infections (i.e., they download/install additional malware). Spam campaigns are used to send thousands of deceptive emails with dangerous files attached to (or linked inside) them. These attachments come in various formats (e.g. archive and executable files, PDF and Microsoft Office documents, JavaScript, etc.). When the files are opened, the infection process is initiated. Rather than activating licensed products, illegal activation ("cracking") tools can download/install malicious software. Rogue updaters infect systems by exploiting flaws of outdated programs and/or simply installing malware rather than the promised updates. Untrustworthy download sources such as unofficial and free file-hosting sites, P2P sharing networks (BitTorrent, eMule, Gnutella, etc.) and other third party downloaders can offer disguised or bundled, malicious programs.

Threat Summary:
Name CU virus
Threat Type Ransomware, Crypto Virus, Files locker.
Encrypted Files Extension .CU (files are also appended with a unique ID and the cyber criminals' email address).
Ransom Demand Message FILES ENCRYPTED.txt and the text presented in the pop-up.
Cyber Criminal Contact cyberunion@tuta.io and cyberunionn@protonmail.com
Detection Names Avast (Win32:RansomX-gen [Ransom]), 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 the computer, previously functional files now have a different extension (for example, my.docx.locked). A ransom demand message is displayed on the desktop. Cyber criminals demand payment of a ransom (usually in bitcoins) to unlock 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

Do not open suspicious or irrelevant emails. Any attachments or links present in dubious messages should also remain opened, as they are the potential source of an infection. Use only official and verified download channels. Programs should be activated and updated with tools/functions provided by legitimate developers. Illegal activation tools ("cracks") and third party updaters are high-risk and should be avoided. Have a reputable anti-virus/anti-spyware suite installed and kept updated. Furthermore, this software should be used for regular system scans and removal of detected threats/issues. If your computer is already infected with CU, we recommend running a scan with Malwarebytes for Windows to automatically eliminate this ransomware.

Text presented in CU ransomware pop-up:

YOUR FILES ARE ENCRYPTED
Don't worry,you can return all your files!
If you want to restore them, follow this link:email cyberunion@tuta.io YOUR ID 1E857D00
If you have not been answered via the link within 12 hours, write to us by e-mail:cyberunionn@protonmail.com
Attention!
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 CU text file ("FILES ENCRYPTED.txt"):

CU ransomware text file (FILES ENCRYPTED.txt)

Text presented in this file:

all your data has been locked us
You want to return?
write email cyberunion@tuta.io or cyberunionn@protonmail.com 

Screenshot of files encrypted by CU (".CU" extension):

Files encrypted by CU ransomware (.CU extension)

CU 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 CU 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 CU 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 CU 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 CU 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 CU, 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 CU 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, and 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 CU 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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Removal Instructions in other languages
Malware activity

Global malware activity level today:

Medium threat activity

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

QR Code
CU virus QR code
A QR code (Quick Response Code) is a machine-readable code which stores URLs and other information. This code can be read using a camera on a smartphone or a tablet. Scan this QR code to have an easy access removal guide of CU virus on your mobile device.
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