Threat Description



Category: Malware
Platform: W32
Aliases: Sinit, Backdoor.Win32.Sinit.f


Sinit is a backdoor that opens a random UDP port and allows unauthorized access to infected machine. According to reports, this port can be used as a part of peer-to-peer network enabling uncentralized distribution of malware to infected computers.


Automatic action

Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.

More scanning & removal options

More information on scanning or removal options is available in the documentation for your F-Secure security product on the Downloads section of our Home - Global site.

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

Contact Support

For further assistance, F-Secure customers can request support online via the Request support or the Chat forms on our Home - Global site.

Technical Details

System installation

When run, the backdoor copies itself to the System directory as 'svcinit.exe'. It adds the following registry key to ensure it will be executed when the system is started:

[HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]  "Userinit" = "%System%\userinit.exe,%System%\svcinit.exe"   

If the system is running windows 9x (95, 98 or ME), it uses the following key instead:

[HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunServices]  "SVC Service" = "%System%\svcinit.exe"   

Sinit opens two UDP ports, port 53 and a random port. Using these ports, the backdoor can receive updates and other programs. It should be noted that domain name protocol (DNS) also uses UDP port 53, but the protocol is completely different.

The backdoor also opens a TCP port 53 which acts as a simple HTTP server. When a HTTP GET request for 'ks.exe' or 'kx.htm' is received, the backdoor sends a copy of itself.


F-Secure Anti-Virus detects various variants of the Sinit backdoor starting with the following update:

Detection Type: PC
Database: 2003-04-25_01

Description Details: Jarkko Turkulainen, June 22th, 2005


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