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.
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