I have seen this happen a few times this year, computer repair shops finding child porn on peoples computers and turning them in. This may be a good thing, but: This is no accident and they do not go around looking for child porn, they are in fact going through your personal files snooping on you and looking for interesting content so they can make copies for themselves. This could be your family trip to the beach they are saving. It could be all your passwords, credit card numbers, tax returns, your whole life. Most of all this data on your hard-drive will fit on a disc so they can go through all your personal files at will forever, or they can sell your information later so you’ll never know where the breach came from.
So I would suggest people ask about this when you take it in, are they going to be going through your personal files. Myself, I wouldn’t take it in to begin with but if I had to I would reformat the hard-drive so they couldn’t steal my content and personal information like credit card numbers. It’s no different than hiring a home repairman, or a house cleaner and them going through your drawers, safe and personal information.