The files are being created by Microsoft Antispyware program (MSA). I know someone from The University of Colorado and they have a public machine with 600+ users/day and themachine is power cycled daily. After a month of using the MSA program on the machine these temporary files occupied 1.1GB of disk space. The MSA program is not cleaning up after itself. It is creating two new temporary files for each new user after a power cycle.
The file all begin with ~DF with a tmp extension.