Possible Duplicate:
Securely format a hard drive
How to wipe a USB hard drive
What is a freeware app i can use to wipe a HD? I have two
1) My external which is <1yr old and is reported 'failure' on disk health checks (maybe i wont bother wiping this?)
2) My laptop which i may send in for repairs or get it replace. It currently is under warranty.
I think i could just write a program that writes random bytes to the HD until i have no space. Would this be good enough? (This app wont work on the broken/external HD tho).