Threat Descriptions

Tenga.A

Classification

Category :

Malware

Type :

Virus

Platform :

W32

Aliases :

Tenga.A

Summary

Tenga.A is a virus that infects files by appending itself to each Windows executable file it finds. The virus also has the ability to scan the network and infect files found in open network shares.

Removal

Tenga is a network-aware parasitic file infector, so the following steps should be taken to disinfect it:

  • Stop network sharing or kill all network connections
  • Set 'Disinfect Automatically' disinfection action for on-access (real-time) scanner of F-Secure Anti-Virus
  • Scan all available hard drives with F-Secure Anti-Virus
  • Disinfect all infected files, delete or rename all undisinfectable files (you have to select 'Delete' or 'Rename' action manually if required)
  • Restart the computer
  • Scan all hard drives again to make sure that there are no more infected files left, repeat disinfection procedure if necessary
  • Disinfect all infected computers connected to the same network
  • Re-enable sharing or reconnect to the network.

Please note that a single infected computer can re-infect the whole network. So make sure that all infected computers are cleaned before they are reconnected to the network.

It is recommended to check whether Windows operating system on all computers has every necessary service pack and security updates. The missing updates and service packs should be installed if needed.

It is also recommended to set strong network share passwords. This greatly limits the spreading of network-aware worms.

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

Tenga.A infects files by appending itself to each Windows executable file it finds. The virus also has the ability to scan the network and infect files found in open network shares.

Upon execution, it connects to and tries to download and execute http://utenti.lycos.it/[***]/dl.exe. It also connects to http://[***].users.freebsd.at and opens a remote command shell on the affected machine on port 54321.

The virus uses CRC matching to search for the required APIs it needs to do its malicious tasks. It avoids infecting ntoskrnl.exe and marks each infected executable files with the character `V´ in the old DOS stub header. The marking of the infected files prevents re-infection attempts

Tenga.A also elevates its privileges and disables Windows File Protection. To check if an instance of itself is already running, the virus creates a mutex named gaelicum.