When I was a victim it was advised to me to change the hard-disk and when asked they said changing OS is not the permanent fix. Can you explain which one is the right.
Probably because of those "
low-level viruses" that can infect at binary level.
High-level format, aka: "
format disk" or "
delete partition" doesn't actually delete most of the files' traces, that's why it's possible to recover them using deleted file recovering tools.
Low-level format (
zero-fill) should work in those cases, but that involves professional software tools.