Threat description



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


Automatic action

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

More scanning & removal options

More information on the scanning and removal options available in your F-Secure product can be found in the Help Center.

You may also refer to the Knowledge Base on the F-Secure Community site for more information.

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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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