Net-Worm:W32/Koobface.CY, TR/Dldr.Agent.atbf.1 (Avira), W32/Koobfa-Gen (Sophos), Worm:Win32/Koobface.gen!A (Microsoft), W32/Koobface.worm (McAfee), W32.Koobface.B (Symantec)


This malware is installed via a fake YouTube webpage (where it is posing as a Flash player update) displayed by Net-Worm:W32/Koobface.CZ.The purpose of this malware is to post comments with HTML links in various online networking locations in order to spread itself.

Automatic action

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Suspect a file is incorrectly detected (a False Positive)?

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 detection database 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.

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Submit a sample

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Technical Details

The following sites are referenced in the body of Koobface.CY:


The routines in Koobface.CY directly target Facebook and the other sites are not used by this variant.


Upon execution, the malware will create these files:

  • %windir%\bolivar28.exe- Copy of the malware
  • %windir%\fmark2.dat- Malware's data file
  • c:\1.reg- Contains a routine to add entries to the registry
  • c:\64234543.bat- Cleanup routine

It will also display this fake error message:

The malware will then add this entry to the registry so that it will be able to insert an HTML page into another HTML page; this ability can be used to insert comments in user pages inside networking sites.

  • HKEY_CLASSES_ROOT\Mime\Database\Content Type\application/xhtml+xml"CLSID"="{25336920-03F9-11cf-8FD0-00AA00686F13}""Extension"=".xml""Encoding"=hex:08,00,00,00


Once installed, Koobface.CY will send an HTTP POST message to this location in order to retrieve the information that it will use as comments:


The site also contains the malware download location. The information and download location are combined to form the messages the worm will post to all of the infected user's contacts on the social interaction site.In addition, Koobface.CY contains a routine to connect to these locations:


The gen.php location also contains information that can be posted as comments on different websites.


Koobface.CY is packed with UPX.