Howtogeek posted a guide about securing your Linux PC by encrypting your hard drive

There's bound to be data on your computer that you want to protect from hackers, nosy friends, or curious colleagues. Encrypting your computer drive protects you from intruders, and here's a couple of different ways to secure your data.
For today's lesson we'll show you how to secure data by encryption a partition, a folder, and also how to create a hidden volume with TrueCrypt.

  How to Secure Your Linux PC by Encrypting Your Hard Drive