Threat description




A remote administration utility which bypasses normal security mechanisms to secretly control a program, computer or network.


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.

Contact Support

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

Technical Details

This malware installs a rootkit onto the system. In addition to hiding its presence on the system, the rootkit is able to inject a dropped file into a process, which is then able to function as a backdoor program.

Installation & Rootkit

During installation, this malware creates a copy of the file %System%\ADVAPI32.DLL as:

  • %Temp%\TDSS%randchar2%.tmp.

It then modifies this file with 21 bytes at the entry point, in order to load the file %Temp%\TDSS%randchar1%.tmp. A number of additional changes must take place for this to occur.

First, the malware deletes the "\KnownDlls\advapi32.dll" section object of the Windows Operating System, in order to remove the legitimate advapi32.dll. The section object is then recreated and linked to the %Temp%\TDSS%randchar2%.tmp file. It then stops and restarts the "MSISERVER" Windows service, which subsequently loads the %Temp%\TDSS%randchar2% file.

The cumulative effect of these changes causes %Temp%\TDSS%randchar1%.tmp to be loaded as a Windows service, which then creates a file, %systemdir%\drivers\TDSServ.sys. This sys file is the actual rootkit driver file. The rootkit hides all its files, as well as registry components beginning with the string 'TDSS'.

The loaded rootkit driver then drops a dll file in the %systemdir% as "TDSSl.dll". It injects the dropped file into SVCHOST.EXE and tries to connects to a number of websites, which are still live at time of writing.

The injected dll can also function as a backdoor, which may be commanded to perform any of the following routines:

  • Download and execute programs
  • Display pop-up advertisements
  • TDSS%randchar1%.tmp is the first temporary file created with random characters added as part of the filename
  • TDSS%randchar2%.tmp is the second temporary file created with different random characters added as part of the filename
File System Changes

Creates these files:

  • %Temp%\TDSS%randchar1%.tmp
  • %Temp%\TDSS%randchar2%.tmp
Process Changes

Creates these mutexes:

  • \TdlStartMutex
Network Connections

Attempts to connect with HTTP to:

  • hxxp://[...]/main
  • hxxp://[...]/main
  • hxxp://[...]/main
  • hxxp://[...]/main
  • hxxp://[...]/main
  • hxxp://[...]/main
  • hxxp://[...]/main
Registry Modifications

The rootkit driver is registered with the key:

  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\TDSSserv.sys

It may also create the following registry subkeys:


The malware creates the following registry entries:

  • HKEY_LOCAL_MACHINE\SOFTWARE\TDSS, build = "standart"
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\tdssdata, affid = "5"
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\tdssdata, subid = "1"
  • HKEY_LOCAL_MACHINE\SOFTWARE\TDSS, serversdown = [dword value]

A mutex is then created so that only one copy of the malware will reside in memory at any given session.

Submit a Sample

Suspect a file or URL was wrongly detected? Send it to our Labs for further analysis

Submit a Sample

Give And Get Advice

Give advice. Get advice. Share the knowledge on our free discussion forum.

More Info