is it true that EVERYTHING that is ever on a HDD can still be read even after FDISKed/being deleted/recorded over?

and that its possible too "deep read" data after its been erased?

my friend sed that it is....(same friend who sed that M4A files have RIAA trackers /virruses in them)..and that its why the governmet melts down all of its HDDs that they throw away...

is this true? and can you get your files back after a reformatt? or after the disk has a giant woofer magnet sat on top of it?

is it true that data stays on your hard drive FOREVER???