Strong enough magnet works like a charm, read that some warez groups actually keep this stuff near their server racks so they can just put them over the HDD's in case of getting busted
It would probably take a very strong one to corrupt data entirely so that even a police lab can't read it with their equipment, probably not something available for puchase in your average hardware store..
It would probably take a very strong one to corrupt data entirely so that even a police lab can't read it with their equipment, probably not something available for puchase in your average hardware store..