After OSX BIOS virus, what's next?
Apparently someone has come up with a rootkit that installs its self on Harddisk's firmware and thus survives reformats and OS reinstalls.
Once upon a time, the best a virus could do was to install over partition table and thus survive a format, but not a partition table rewrite.
Things have progressed a lot since then.
Link to the claim:
http://www.malwaretech.com/2015/06/hard-disk-firmware-rootkit-surviving.html