Eraser 5.3 - Erase data permanently. Free.

Eraser is an advanced security tool, which allows you to completely remove sensitive data from your hard drive by overwriting it several times with carefully selected patterns.

You can drag and drop files and folders to the on-demand eraser, use the convenient Explorer shell extension or use the integrated scheduler to program overwriting of unused disk space or, for example, browser cache files to happen regularly, at night, during your lunch break, at weekends or whenever you like.

The patterns used for overwriting are based on Peter Gutmann's paper "Secure Deletion of Data from Magnetic and Solid-State Memory" and they are selected to effectively remove the magnetic remnants from the hard disk.

Other methods include the one defined in the National Industrial Security Program Operating Manual of the US Department of Defense and overwriting with pseudo-random data. You can also define your own overwriting methods.