W97M/Reiz is a destructive Word trojan.
When a trojan document is opened, it creates a batch file, "Autoexek.bat", and an AutoRun file to the root of the "C:" drive.
When Windows is restarted, the AutoRun is enabled and when the "C:" drive is accessed via Windows Explorer or My Computer the batch file is executed.
The batch file shows a message:
Updating! This May Take A While... Please Wait...
and then attempts to remove everything from the "C:" drive using "Deltree" command.
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.