Threat Descriptons



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Type :


Aliases :

Sdbot.RPC.A, W32/Spybot.worm.lz, W32.Randex.E, WORM_RPCSDBOT.A


Sdbot.RPC.A is an IRC controlled backdoor which contains spreading routines exploiting the MS03-026 (also known as DCOM/RPC) vulnerability.


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

System infection

After entering the system Sdbot.RPC.A installs itself with the following steps:

  • Copies the worm to the System Directory as 'winlogin.exe'
  • Adds 'winlogin.exe' to the registry to the following value
  • Drops the main DLL component to the System Directory as 'yuetyutr.dll'
  • The DLL is loaded into the running explorer.exe process
  • Modifies system.ini:
     [Boot] Shell=explorer.exe winlogin.exe 	
  • Adds several values to the registry:
     'HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce\winlogon' 'HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\winlogon'


The backdoor code is based on Sdbot. It connects to a predefined IRC server and joins a channel and waits for commands. Commands it supports provide full access to the compromised computer.

With one of the commands the backdoor can be instructed to scan for vulnerable hosts using the DCOM/RPC exploit. If a vulnerable host is found Sdbot.RPC.A infects the host.

More information on the DCOM/RPC (MS03-026) vulnerability is available at

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