Thermite will do the trick nicely and is more fun than cat litter, according to a private communication from the national association of pyromaniacs. http://en.wikipedia.org/wiki/Thermite http://www.petitiononline.com/HUNGSOLS/petition.html
To keep even the NSA or the Russian Mafia from deciphering it, just make sure you do this: BEFORE doing this:
I believe Evidence Eliminator is the original disk wipe clean software and it's come with a 30 day trial. Do a google search.
Why not fill it up with giant garbage data/files? event-management-systems.info callcenter-career.info callcenter-courses.info