they don't need to trace it to your hard drive, they only need to trace it to your IP address. which by the time the data enters your house it has already been logged to your IP address.
Also destroying the drive or the data doesn't help because they don't need the data, the just need the log that says what you were downloading, and that is stored on a server at the ISP.
and they are totally looking for people that are downloading for personal use. they prefer to go after the big dogs first of course. but the MPAA and RIAA go after personal users a lot because they are downloading from the big dogs. kinda like how cops like to go after big drug dealers, but they go after little drug dealers and the end users too!