On the topic of online security, Facebook is one site that has an enormous amount of personal information. A lot of Facebook accounts have been hacked lately, including Mark Zuckerberg's personal page. Most of the time, these can be avoided by using Facebook's new security feature:
Simply go to your Account, then click on Account Settings
Expand the Account Security section, check the box that says Secure Browsing (HTTPS).
Save your settings. And you're all done. Unfortunately, some apps, like Networked Blogs, do not support HTTPS yet so you'll have to repeat this procedure every time you use an app that disabled this security setting.