Sometimes at office or even at home i don't want certain part of my hard drive not accessible by anyone. Well you can hide your folders but is it giving you the optimal protection, i don't think so. TrueCrypt is a open source software comes with a highly secured protection systems. The algorithms are so difficult to break that it might take a few billion years to break the password. TrueCrypt can be used on windows xp/vista or linux platforms. Actually what it do is to create a physical file on a hard disk and encrypt it with very strong protection and load that file as a virtual drive. TrueCrypt also can be used to protect your USB or Flash disks.