Threat Descriptons



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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.


Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note: You need administrative rights to change the settings.

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
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