Worm:W32/Tyhos regularly checks for any removable devices connected to the system; if found, the worm copies itself to the removable drive.


Automatic action

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.

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Technical Details

Worm:W32/Tyhos spreads via infected removable drives; once present on a machine, it checks the system for any connected removable drives every 10555 milliseconds. If found, it copies itself to the removable drive.

The worm file itself is packed using the F[ast] S[mall] G[ood] packer.

The details below are based on analysis of the following sample: SHA1: 21ae5cf02ba792d902efb7cbc9a115769c878337.


On execution, the worm creates copies of itself in the following locations:

  • %System%\[random number]\avgupdate.exe
  • %System%\[random number]\isass.exe

The copied files have their properties set to hidden. The worm also adds registry keys for both files, so that they run automatically whenever the system is started:

  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\avpupdt = "%System%\[Random_Numbers]\avgupdt.exe"
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\ctfmon = "%System%\[Random_Numbers]\lsass.exe"

It also drops an HTML page to:

  • %SystemRoot%\index.html

And creates the following mutexes:

  • ----[ GHOSTY.NET ]----
  • 6H0sty-Gh057y.net-ghozty

Once the files are dropped, the isass.exe file is launched by shellexecute and checks whether a file named ghosty.d is present in the SystemRoot folder. It also opens the dropped index.html file:

index.html file displayed by Worm:W32/Tyhos

Date Created: -

Date Last Modified: -