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.


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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.

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