Home > Threat descriptions >

Worm:W32/Sobig.F

Classification

Category: Malware

Type: Worm

Aliases: Worm:W32/Sobig.F

Summary


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.

Removal


Automatic action

Based on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the detected program or file, or ask you for a desired action.

Knowledge Base

Find the latest advice in our Community Knowledge Base.

About the product

See the manual for your F-Secure product on the Help Center.

Contact Support

Chat with or call an expert for help.

Submit a sample

Submit a file or URL for further analysis.

Technical Details


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 emails 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