Make Your Facebook Account Private

(by: Wired How-To Wiki)

Facebook recently (in December, 2009) unveiled a radically revamped set of privacy controls. They are better and more forward-thinking than its previous efforts, but Facebook made one very important change in late 2009: almost all user data is now made public by default.
Facebook users were asked to verify their privacy settings using Facebook's "Privacy transition tool" that recommended some default settings. Oddly, the suggested defaults made most profile settings, photo uploads, status updates and application settings viewable by everyone on the internet. This means the whole world could see everything Facebook users post if they didn't change the defaults.

For more details on these privacy changes, see the Electronic Frontier Foundation's overview.
The most invasive part of the policy for most people will be the public search results settings. This means if they post something and later decide they want to switch to a private profile, those embarrassing posts will remain in search engine indexes.
The good news is that Facebook actually now offers more fine-grained controls over which bits of personal information you share than ever before. The bad news is that the high level of control makes preserving your privacy a fairly complex process. There isn't a simple check box that says "make my profile private."
But fear not, we've got you covered. Follow these instructions below.

Locking down your profile

Head to your privacy settings under the Account menu at the upper right corner of your Facebook page.
On the privacy settings page, you'll see five categories: Profile, Contact Information, Applications and Websites, Search and Block List.
Start at the top with Profile information and change all the options to "Friends." This will stop people you don't know from accessing any of your personal data.

Do the same for your contact information, most of which, thankfully, still defaults to Only Friends.
Also be aware that each setting has a "customize" option which allows you to, for example, set your information to "visible only to friends" but also block certain "friends" (like your mom, so she won't see the drunken, late night rants you post on your Wall).

Applications and outside data

What you post to Facebook doesn't just show up on Facebook anymore. Your status updates and photos go out over a vast network of connected websites and applications, all linked together through Facebook Connect and Facebook's App Platform.
This is one area that many people overlook, but it has perhaps the greatest potential to unwittingly leak information about you.
Head to the "Applications and Websites" area of Privacy Settings and adjust the settings to "Friends Only."
But there's more. Click the "Edit Settings" button for the "What your friends can share about you" section and uncheck anything you aren't comfortable seeing leak out of Facebook.
Finally, head to the "Search" section of your Privacy Settings and uncheck the box that allows search engines to index your posts. That way, when people search for your name on the internet, they only see public content, and not anything you wrote to your friends on Facebook. Likewise, when people run image searches for you on web search engines, they won't see any Facebook photos.

Conclusion

It takes a little bit of work to lock your data down. But if you'd like to keep Facebook the private, for-your-eyes-only social network it once was, you still can.