I recently learned that Facebook added the option of using HTTPS. HTTPS is a secure version of HTTP, the dominant and near-universal protocol for internet data transfer. Basically by using HTTPS, all messages will be encrypted when enabled.
To help make Facebook more secure, the site is introducing a new encryption option that uses the same security technology that shopping sites employ to keep hackers from seeing credit card numbers.
To turn on secure Facebook browsing, log in to Facebook and click on Account in the upper right corner. Select Account Settings. On that page near the bottom, click on Account Security. If the new option has been made available to your account, the first option at the top will be Secure Browsing (https). Click that, then hit the blue Save button just below it. You’re done.
HTTPS is not unbreakable, but cracking it is far more work than anyone is likely to do.
Source: N.Y. Times Blog