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Aliases :

Backdoor:W32/Tofsee.H, Backdoor:W32/Tofsee.A!Mem


Backdoor:W32/Tofsee silently uses the user's machine to send out spam emails and messages, mine for virtual currency and perform other malicious activities, as directed via instructions from a remote server.


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

Backdoor:W32/Tofsee may be found being offered on websites, or dropped on the user's machine as part of the payload of another malware. Tofsee's executable file is distributed with a Flash Player icon, as a decoy to lure the unsuspecting user into clicking it and launching the malware.


When Tofsee is executed, it first creates a copy of itself in the following location:

  • %USERPROFILE%random_generated_strings.exe

And creates the following registry key to make sure this copy is executed each time the computer is started up:

  • HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Run "MSConfig" = "%USERPROFILE%random_generated_strings.exe"

Next, the malware creates and runs a new thread in the 'svchost.exe' process and adds itself as a 'trusted program' to the Windows Firewall. Finally, it deletes the original executable file to cover its own tracks.


Once Tofsee has added itself as a trusted program, it can safely communicate with a remote Command and Control (C&C) server to obtain additional instructions, as well as download several plug-ins or modules that it loads into memory. These allow the malware to:

  • Create spam emails and send them through an SMTP server via a HTTP proxy
  • Send spam in Facebook, Skype and Twitter (in postings, tweets, etc)
  • Participate in a Distributed Denial of Service (DDoS) attack
  • Mine for virtual currency such as Litecoin

And so on, as per directions received from the C&C server.