There is a free program called, I think, "Shredder." Shred your files, don't just delete time. Especially shred "junk" emails.

Unless you melt your drive into a blob a governmental agency can restore your files IF they want to take the time, money, and effort to do so. I don't think the baddies can. This applies to all types of drives. The last time I destroyed a couple of hard drives I just punched holes through them and bent their case -- good enough for 'most things.