Worm:W32/Tyhos

Classification

Malware

Worm

W32

Win32.Tyhos

Summary

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

Removal

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.

Find out more

Knowledge Base

Find the latest advice in our Community Knowledge Base.

User Guide

See the user guide for your product on the Help Center.

Contact Support

Chat with or call an expert for help.

Submit a sample

Submit a file or URL for further analysis.

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.

Execution

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: -