WM/Muck is a simple Word macro virus.
It activates when an infected document is opened. Then it infects the global template. After Word has been restated it infects every saved document after that.
Beside replication, it will show a message box from time to time with the following text:
Disinfection & Removal
Allow F-Secure Anti-Virus to disinfect the relevant files.
For more general information on disinfection, please see Removal Instructions.
Technical Details: Sami Rautiainen, F-Secure