TROJ_CRYPCTB.APU
Ransom:Win32/Critroni.A (MICROSOFT), Win32/Filecoder.DA trojan (NOD32)
Windows
![](/vinfo/imgFiles/legend.jpg)
Threat Type: Trojan
Destructiveness: No
Encrypted: Yes
In the wild: Yes
OVERVIEW
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 uses Windows Task Scheduler to create a scheduled task that executes the dropped copy.
TECHNICAL DETAILS
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.
Installation
This Trojan drops the following copies of itself into the affected system and executes them:
- %User Temp%\kpigvia.exe
(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)
It drops the following files:
- %User Profile%\My Documents\Decrypt All Files {random extension}.bmp - wallpaper used by the malware
- %User Profile%\My Documents\Decrypt All Files {random extension}.txt - contains the ransom note
- %User Profile%\My Documents\{random file name}.html - contains list of encrypted files
- %Windows%\Tasks\zqmdnyk.job
(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.. %Windows% is the Windows folder, where it usually is C:\Windows on all Windows operating system versions.)
It uses Windows Task Scheduler to create a scheduled task that executes the dropped copy.
Autostart Technique
The scheduled task executes the malware every:
- at logon
Other System Modifications
This Trojan modifies the following registry entries:
HKEY_CURRENT_USER\Control Panel\Desktop
Wallpaper = "%User Profile%\My Documents\Decrypt All Files {random extension}.bmp"
(Note: The default value data of the said registry entry is {user-defined}.)
Other Details
This Trojan renames encrypted files using the following names:
- {original file name and extension}.{random 7-letter}
SOLUTION
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
Step 4
Restore this modified registry value
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\Control Panel\Desktop
- From: Wallpaper = "%User Profile%\My Documents\Decrypt All Files {random extension}.bmp"
To: Wallpaper = "{user-defined}"
- From: Wallpaper = "%User Profile%\My Documents\Decrypt All Files {random extension}.bmp"
Step 5
Search and delete this file
- %Windows%\Tasks\zqmdnyk.job
- %User Profile%\My Documents\Decrypt All Files {random extension}.bmp
- %User Profile%\My Documents\Decrypt All Files {random extension}.txt
- %User Profile%\My Documents\{random file name}.html
Step 6
Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_CRYPCTB.APU. 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.
NOTES:
Restore the encrypted files by this malware from backup. Note that the encrypted files have the extension .{random 7-letter}.
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