One one of my clients got a very nasty virus called Win32.runouce (Avast Name) a variation of the W32/Chir. What this virus does is creates big amount of tmz****.tmp files that infected with a trojan file pp.exe. Also modifies registry keys and infect other executables files.
Even after you have the system cleaned by your anti virus and/or manually this virus leave lots of .eml files. These .eml files are generally email files but in this case are left overs from this virus.
The whole point here is that even after the system is supposedly cleaned you still cannot delete these files within Windows 7 operating system. If you search for these files the results might come out hundreds or thousands of them. You can select them but Windows Explorer will not give you the option to delete!