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Virus:TR/Skelf.A
Date discovered:17/05/2012
Type:Trojan
In the wild:No
Reported Infections:Medium to high
Distribution Potential:Low
Damage Potential:Medium
Static file:Yes
File size:34.477 Bytes
MD5 checksum:78EE9C318793ADB145A5ABDC07DB8F1B
VDF version:7.11.30.90 - Thursday, May 17, 2012
IVDF version:7.11.30.90 - Thursday, May 17, 2012

 General Method of propagation:
   • No own spreading routine


Aliases:
   •  Eset: Win32/Trustezeb.B
     DrWeb: Trojan.Winlock.5908


Platforms / OS:
   • Windows 2000
   • Windows XP
   • Windows 2003
    Windows Vista
    Windows 7


Side effects:
   • Lowers security settings
   • Registry modification


Right after execution the following information is displayed:


 Files It copies itself to the following locations:
   • %TEMPDIR%\%random character string%.pre
   • %SYSDIR%\%random character string% .exe
   • %APPDATA%\%random character string%\%random character string%.exe



It deletes the initially executed copy of itself.

 Registry The following registry keys are added in order to run the processes after reboot:

HKCU\Software\Microsoft\Windows\CurrentVersion\Run
   • %random character string% = %APPDATA%\%random character string%\%random character string%.exe

HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
   • "Userinit"="%SYSDIR%\userinit.exe,%SYSDIR%\%random character string%.exe,"



The following registry key including all values and subkeys is removed:
   • [HKLM\SYSTEM\CurrentControlSet\Control\SafeBoot]



The following registry keys are added:

HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\
   Image File Execution Options\msconfig.exe
   • "Debugger"="%random character string%.EXE"

HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\
   Image File Execution Options\regedit.exe
   • "Debugger"="%random character string%.EXE"



The following registry keys are changed:

Disable Regedit and Task Manager:

HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system
   New value:
   • "DisableTaskMgr"=dword:00000001
   • "DisableRegedit"=dword:00000001

HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System
   New value:
   • "DisableRegistryTools"=dword:00000001
   • "DisableRegedit"=dword:00000001
   • "DisableTaskMgr"=dword:00000001

 Injection It injects itself as a remote thread into a process.

    Process name:
   • %SYSDIR%\ctfmon.exe

   If successful, the malware process terminates while the injected part remains active.

 File details Runtime packer:
In order to aggravate detection and reduce size of the file it is packed with the following runtime packer:
   • UPX


Encryption:
Encrypted - The virus code inside the file is encrypted.

Description inserted by Ana Maria Niculescu on Thursday, May 17, 2012
Description updated by Andrei Gherman on Thursday, May 17, 2012

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