So, you think you cleaned all your personal files from that old computer you got rid of?

Two graduate students at the Massachusetts Institute of Technology suggest you think again.

Over two years, Simson Garfinkel and Abhi Shelat bought 158 used hard drives at secondhand computer stores and on eBay. Of the 129 drives that functioned, 69 still had recoverable files on them and 49 contained "significant personal information" -- medical correspondence, love letters, pornography and 5,000 credit card numbers. One even had a year's worth of transactions with account numbers from a cash machine in Illinois.

About 150,000 hard drives were "retired" last year, according to the research firm Gartner Dataquest. Many end up in the trash, but many also find their way back onto the market.

Over the years, stories have surfaced about personal information turning up on used hard drives, raising concerns about privacy and the danger of identity theft.

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