Threat Description

Worm:​W32/Sobig.F

Details

Aliases: Worm:​W32/Sobig.F
Category: Malware
Type: Worm
Platform: W32

Summary



A standalone malicious program which uses computer or network resources to make complete copies of itself. May include code or other malware to damage both the system and the network.



Removal



Automatic Disinfection

Allow F-Secure Anti-Virus to disinfect the relevant files.

For more general information on disinfection, please see Removal Instructions.



Technical Details



A new variant of Worm:W32/Sobig, known as Sobig.F was first found on August 19th, 2003 and it is spreading in the wild.

The executable has a size of around 70KB and it is packed with TELock. It has its own SMTP engine, apart from routines to query directly DNS servers and make requests using the Network Time Protocol.

The worm also has updating capabilities. It will attempt to download updated versions when certain conditions are met. The worm will stop spreading on 10th of September 2003. From this date onwards the worm will exit immediately when executed.

Infection

It will install itself into:

  • %windir%\winppr32.exe

Proceeding then to add the following keys to the Windows Registry:

  • [HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run] "TrayX" = %windir%\winppr32.exe /sinc
  • [HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run] "TrayX" = %windir%\winppr32.exe /sinc

So it starts when Windows does.

Mail spreading

The worm usually arrives in e-mails with the following characteristics:

From:The 'From:' field is filled with an address found from the infected system. If no address is found, it will use "admin@internet.com"

To:

The 'To:' field is filled with an address found from the infected system.

Subject:

Any from the following list:

  • Re: Thank you!
  • Thank you!
  • Your details
  • Re: Details
  • Re: Re: My details
  • Re: Approved
  • Re: Your application
  • Re: Wicked screensaver
  • Re: That movie

Body:

It chooses one from the two following lines:

  • See the attached file for details
  • Please see the attached file for details.

Attachment name:

The name is selected from the following list:

  • your_document.pif
  • document_all.pif
  • thank_you.pif
  • your_details.pif
  • details.pif
  • document_9446.pif
  • application.pif
  • wicked_scr.scr





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