TrueCrypt is free software that encrypts data “on-the-fly”. You can create an encrypted hard drive, a separate partition or a directory. TrueCrypt is portable — it works on GNU/Linux and Windows. Worried about someone getting into your private files when your laptop gets stolen? Don’t wait encrypt your data now.

Oh, by the way, TrueCrypt is Open Source and free, so this post may sound like an ad but there is no profit in it for anyone, just wanted to let you know that it is out there. At the time of writing, 2,777,511 users had downloaded the program with 5000 people a day truly encrypting their files and that counts only those who are getting it from the source and not the mirrors.