Analysis by: Rika Joi Gregorio


Trojan-Ransom.Win32.Crypren.pzj(Kaspersky), Ransom:MSIL/Glock.A(Microsoft), RDN/Ransom!ej(McAfee), Troj/dnRan-A(Sophos), a variant of MSIL/LockScreen.JV trojan(Eset), Trojan.MSIL.LockScreen(Ikarus)


Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)


  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes


Infection Channel: Dropped by other malware

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It connects to certain websites to send and receive information.


File Size: 140,800 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 06 Sep 2014
Payload: Changes users' wallpaper, Displays message/message boxes

Arrival Details

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.


This Trojan drops the following files:

  • {malware path}\filelist.txt - contains list of the original file name of the encrypted files

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

CLock = "{malware path and file name}"

Process Termination

This Trojan terminates the following processes if found running in the affected system's memory:

  • regedit.exe
  • tasmgr.exe
  • procexp.exe
  • msconfig.exe
  • rstrui.exe

Information Theft

This Trojan gathers the following data:

  • HWID
  • Computer Name
  • User Name

Other Details

This Trojan connects to the following website to send and receive information:

  • www.{BLOCKED}
  • www.{BLOCKED}

It encrypts files with the following extensions:

  • .3fr
  • .accdb
  • .arw
  • .bay
  • .bmp
  • .cdr
  • .cer
  • .cr2
  • .crt
  • .crw
  • .dbf
  • .dcr
  • .der
  • .dng
  • .docm
  • .docx
  • .doc
  • .dwg
  • .dxf
  • .dxg
  • .eps
  • .erf
  • .exif
  • .gif
  • .indd
  • .jfif
  • .jpeg
  • .jpg
  • .kdc
  • .mdb
  • .mdf
  • .mef
  • .mp3
  • .mrw
  • .nef
  • .nrw
  • .odb
  • .odc
  • .odm
  • .odp
  • .ods
  • .odt
  • .orf
  • .p12
  • .p7b
  • .p7c
  • .pdd
  • .pdf
  • .pef
  • .pem
  • .pfx
  • .png
  • .pptm
  • .pptx
  • .ppt
  • .pptx
  • .psd
  • .pst
  • .ptx
  • .r3d
  • .raf
  • .raw
  • .rtf
  • .rw2
  • .rwl
  • .sr2
  • .srf
  • .srw
  • .txt
  • .wb2
  • .wpd
  • .wps
  • .x3f
  • .xlk
  • .xlsb
  • .xls
  • .xlsm
  • .xlsx

It renames encrypted files using the following names:

  • {original file name and extension}._clf


After successfully encrypting files on the targeted system, it replaces the wallpaper with another image:

It then demands users to pay a fine:

Users can pay via bitcoins:


Minimum Scan Engine: 9.700
VSAPI OPR PATTERN File: 11.131.00
VSAPI OPR PATTERN Date: 06 Sep 2014

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • CLock = "{malware path and file name}"

Step 5

Search and delete this file

[ Learn More ]
There may be some files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • {malware path}\filelist.txt

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_CRITOLOCK.A. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.

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