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:
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
Technical Details: Sami Rautiainen, F-Secure