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Remove CTB-Locker and Restore the Encrypted Files

CTB-Locker, also known as Critoni Ransomware, is a Trojan that encrypts the files on the infected computer and blocks the user’s access to his data. Critoni Ransomware displays a ransom message demanding a high price for the decryption of the files. As researchers have established, the crypto-malware has been for sale on the black market for around 3000 US dollars. Experts warn that the threat is still actively infecting computers worldwide and recommend installing a trustworthy anti-malware tool no your machine and performing regular backups of your important files.

Name CTB-Locker
Type Ransomware
Short Description The cyber-threat encrypts user files leaving a ransom note and asking for 0.2 BTC to decrypt the files.
Symptoms The user may witness his files to become encrypted with the .ctb, .ctbl and .ctb2 as well as random file extensions.
Distribution Method Via exploit kits or Trojans.
Detection Tool Download Malware Removal Tool, to See If Your System Has Been Affected by CTB-Locker
User Experience Join our forum to discuss CTB-Locker.

CTB Locker – How Did I Get Infected

CTB Locker has been reported by Microsoft Malware Protection Center to be spread via exploit kits or a Trojan.Downloader. Exploit kits may be created for plugins such as Java or Flash Player and it is easy to insert malicious code that creates weaknesses in Windows. Furthermore, the Trojan.Downloader that may be used might collect different information about the computer that will be infected so that the infection process is undetected. Such information may be details about the Windows version, type of Antivirus software used, etc. The Trojan may spread via malicious links that may contain drive-by-downloads or malicious attachments sent online.

CTB Locker Ransomware – What Does It Do?

Once it has been downloaded and activated, the ransomware may insert malicious code into the critical Windows process, called svchost.exe. Furthermore it may create randomly named files, such as sz0s8g2h.exe for example, in the following folders:

  • %Temp%
  • %AppData%

According to Microsoft researchers, after it has created its payload files, the ransomware begins to scan for and encrypt files with these file extensions:

3fr 7z abu accdb ai arp arw bas bay bdcr bdcu bdd bdp bds blend bpdr bpdu bsdr bsdu c cdr cer config cpp cr2 crt crw cs dbf dbx dcr dd dds der dng doc docm docx dwg dxf dxg eps erf fdb gdb groups gsd gsf ims indd iss jpe jpeg jpg js kdc kwm md mdb mdf mef mrw nef nrw odb odm odp ods odt orf p12 p7b p7c pas pdd pdf pef pem pfx php pl ppt pptm pptx psd pst ptx pwm py r3d raf rar raw rgx rik rtf rw2 rwl safe sql srf srw txt vsd wb2 wpd wps xlk xls xlsb xlsm xlsx zip

After encrypting the files of users, it may add a suspicious file extension after the files. The following file extensions are reported by researchers from Microsoft and BleepingComputer to be used by CTB Locker:

  • .ctb
  • .ctb2
  • .ctbl
  • Random file extensions(newer versions)

The ransomware then may drop the following files that contain the demands of the cyber-criminals:

  • %MyDocuments%\AllFilesAreLocked{randomuserid}.bmp
  • %MyDocuments%\{randomname}.html
  • %MyDocuments%\DecryptAllFiles{randomuserid}.txt

These files contain the ransom instructions. One of them is the wallpaper that is changed to the following:

encrypted files-ctb-locker-sensorstechforum

The encrypted files contain a decryption key held by the cyber criminals. As other ransomware Trojans, CTB-Locker uses Onion routing (Tor) in order to remain anonymous and protect the cyber-crooks’ identity. The good news is that compared to other crypto-viruses, CTB-Locker does not demand a ransom this high. The ransom amount demanded is 0.2 Bitcoins which is around 120 US dollars.

What is new about this ransomware is that the new variants may use random file extensions to encrypt the files such as .zz2dqj or .9jsaxsf. Upon opening, Windows claims that the questionable files are corrupt, and they cannot be fixed by simply removing the extension for the file. Here is an example of an encrypted file names by CTB-Locker:

  • New Document.docx.ctbl
  • New Picture.jpg.ctb
  • New Presentation.pptx.ctb2
  • New Text Document.vdi.adid2k

Even though paying the ransom money may bring back your files, we strongly advise you NOT to do it, even though the newer variant of CTB decrypts 5 files for free. This funds the cyber-criminals to develop further their virus plus it may be no guarantee that the decryption keys for your files will be sent back to you so you can restore them.

Here is the decryption screen users see when they are following the decryption instructions:

decryption-sensorstechforumSource: Bleeping Computer

Removing CTB-Locker Ransomware Completely

To remove this nasty ransomware virus, you should boot your PC into safe mode and install an anti-malware scanner that will locate its registry entries and restore any scheduled tasks for the malware to run on system start. For maximum effectiveness, it is advisable to download the anti-malware software from a safe PC and install it via offline installer to the infected one while you are offline.

1. Boot Your PC In Safe Mode to isolate and remove CTB-Locker
2. Remove CTB-Locker with SpyHunter Anti-Malware Tool
3. Back up your data to secure it against infections and file encryption by CTB-Locker in the future
Optional: Using Alternative Anti-Malware Tools

Restore Files Encrypted by CTB-Locker Ransomware

Security engineers strongly advise users NOT to pay the ransom money and attempt restoring the files using other methods. Here are several suggestions:

To restore your data, your first bet is to check again for shadow copies in Windows using this software:

Shadow Explorer

If this method does not work, Kaspersky have provided a decryptors for files encrypted with the RSA and other encryption algorithms:

Kaspersky Decryptors

Another method of restoring your files is by trying to bring back your files via data recovery software. Here are some examples of data recovery programs:

EaseUS Data Recovery
Recuva
R-Studio
Photorec

For further information you may check the following articles:
Remove RSA-2048 Key From Crypto Ransomware
Restore Files Encrypted via RSA Encryption

NOTE! Substantial notification about the CTB-Locker threat: Manual removal of CTB-Locker requires interference with system files and registries. Thus, it can cause damage to your PC. Even if your computer skills are not at a professional level, don’t worry. You can do the removal yourself just in 5 minutes, using a malware removal tool.

Berta Bilbao

Berta is the Editor-in-Chief of SensorsTechForum. She is a dedicated malware researcher, dreaming for a more secure cyber space.

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