Black Magnetic Dust
The Internet abounds with quite a lot Do It Yourself materials for data recovery from damaged hard drives. These methods often confuse drive owners and most of them are based on data recovery myths. If you are really lucky, these so-called methods will not damage a drive any further. If you are not, the result can be fatal for the drive and eventually for your data. Black magnetic dust you see on the recirculation filter is an obvious hint that someone was not that lucky. Read-write heads were previously tampered with.