DM.400 is an old and rare virus. It does not seem to do anything but replicate. It contains the following text:
A slightly modified version 1.01 is also known.
Probably an older, more primitive variant.
This variant claims to be version 1.05
Also see: DMSetup.
Allow F-Secure Anti-Virus to disinfect the relevant files.
For more general information on disinfection, please see Removal Instructions.