The nonk 6

Description: It's easy to recover deleted files unless you routinely wipe the file data away. Eraser "overwrites the data area with your choice of random data patterns, and also wipes data in the recycling bin, unused disk space, and a number of other places where data can secretly lurk." Creates an INI file in C:\windows.
Many file cleaners include secure erasing such as CCleaner and Revo Uninstaller. But even if you securely delete files with something like CCleaner, I recommend regular free space wiping to increase the effectiveness of erasure (1 pass is usually enough on modern drives).