Threat Description

Virus: W32/Saburex.A


Category: Malware
Type: Virus
Platform: W32
Date Discovered: December 10, 2006
Aliases: Virus.Win32.Saburex.a


Virus:W32/Saburex.A is an appending file infector virus that may betray its presence by displaying an error message when its infection routine fails to execute. Saborex.A encrypts its strings using a simple XOR routine.


Automatic action

Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.

More scanning & removal options

More information on scanning or removal options is available in the documentation for your F-Secure security product on the Downloads section of our Home - Global site.

You may also refer to the Knowledge Base on the F-Secure Community site for more information.

Contact Support

For further assistance, F-Secure customers can request support online via the Request support or the Chat forms on our Home - Global site.

Technical Details


During installation, the virus copies itself to the Windows folder, then creates several temporary files in the root directory as well as in the system's designated temporary folder. The files contain virus code fragments and hosts file codes used to form newly infected files. It then proceeds to search for and infect files with the following characteristics:

  • 'Fixed Drive' drive type (virus randomly checks for logical drives until it finds this type)
  • .EXE extension
  • file size larger than 80000 hex or 524,288 Bytes

File size checking is done several times and infection is performed utilizing Microsoft Cab APIs.

Saburex.A also searches for files from the root directory using the wildcard *.*

The virus avoids directory or files starting with the following strings:

  • _restore
  • documents and
  • music
  • program files
  • win

To infect a file, Saburex.A overwrites a block in the first section of the host file and hides it by appending it at the end of the last section together with its virus code.


Once the file is infected, the virus drops a DLL component into the temporary folder as:

  • [Random Incremental Number].tmp

The DLL component is then executed using Microsoft rundll32:

  • rundll32 %temp%\[Random Incremental Number].tmp,a [Path and Filename of Infected Executable]

When executed, the DLL drops a copy of itself into the windows system directory using the following names:

  • ole16.dll
  • shell32.dll

If the executed copy is not using the filename of one of the dropped files, the virus will delete the executed copy with the help of a temporary batch file created in the temporary folder with the name:

  • [3 Random Numbers].bat

There are some instances where the malware's DLL component fails to execute due to Windows memory protection. In this case, an error message is likely to appear, which may look as below:


As a launch point, Saburex.A adds the following registry entry:

  • HKEY_CLASSES_ROOT\Software\Classes\CLSID\{00021401-0000-0000-C000-000000000046}\InProcServer32 @ = shell32.dll @ = ole16.dll

Saburex.A checks the following event name to ensure that only one instance of its DLL component is running in memory:

  • ~DF


F-Secure Anti-Virus detects this malware with the following updates:
Database: 2006-12-10_01


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