You need to overwrite the data for it to be completely irrecoverable. I would use that program to overwrite the entire hard drive. I wouldn't even bother formatting it after that, just let whoever buys it format it.
You need to overwrite the data for it to be completely irrecoverable. I would use that program to overwrite the entire hard drive. I wouldn't even bother formatting it after that, just let whoever buys it format it.