Second hand data?
Simply formatting the hard drive of your computer does not remove the files – the process removes the ‘index’ that keeps track of the location of your data on the disc.
That is good news for forensic investigators – a look at the disklabs Web site will show you how much data can be recovered – but bad news if you sell your computer or an older hard drive on the well known online auction site. It may be possible to recover passwords and Web addresses from your old hard drive.
Mac OS X has an option for ‘clean install’ of the operating system – a clean install removes all the data from the hard drive, and you get the option of writing zeros to all the locations on the drive (takes hours…). Even that is not foolproof – military standard software writes random data to each storage location three times over.
For Windows computers or computers that can boot from an MS-DOS system floppy you can use Kill Disc. The free version gives you zeros written to each location – same as Mac OS X.