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:
Depending on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the suspect file, or ask you for a desired action.
More information on the scanning and removal options available in your F-Secure product can be found in the Help Center.
You may also refer to the Knowledge Base on the F-Secure Community site for more information.