Removing PC DM files
Most of these file are usually hosted by mobile phones, trace if you have connected your computer to a phone or other device through a USB or Bluetooth.if no history of such, it might through a file downloaded from the internet or through an insecure browser.
i would suggest first getting a separate virus removal tool like Kaspersky virus removal tool 2010. or any other depending on your choice.Note that virus removal tool is separate from an anti virus. make sure that the anti virus is not currently installed (most antivirus might not be able to detect these type of files as they dont appear like viruses) run the tool and then install the antivirus.
if the problem persist, try creating a backup then formating the drive which contains this virus.