Facebook is a personal vault that can contain photos of your firstborn, plans to bring down your government and, occasionally, a record of your indiscretions.
It can be scoured by police officers, partners and would-be employers. It can be mined by marketers to show tailored advertisements.
And now, with Facebook's newfangled search tool, it can allow strangers, along with "friends" on Facebook, to discover who you are, what you like and where you go.
Facebook insists it is up to you to decide how much you want others to see. And that is true, to some extent. But you cannot entirely opt out of Facebook searches. Facebook, however, does let you fine-tune who can see your "likes" and pictures, and, to a lesser extent, how much of yourself to expose to marketers.
What can you do? Ask yourself four simple questions.
1 How would you like to be found?
Go to "who can see my stuff" on the upper right side of your Facebook page. Click on "see more settings." By default, search engines can link to your timeline. You can turn that off if you wish.
Go to "activity log." Here you can review all of your posts, pictures, "likes" and status updates. If you are concerned about who can see what, look at the original privacy setting of the original post — and decide whether you would like to be associated with them.
If you are concerned about things that might embarrass or endanger you on Facebook — Syrians who endorse the opposition may not want to be discovered by government apparatchiks — comb through your timeline and get rid of them. The only way to ensure that a post or a photo is not found is to "unlike" or "delete" it.
2 What do you want the world to know about you?
Go to your profile page and click "About me." Decide whether you would like your gender, or the name of your spouse, to be visible on your timeline. Think about whether you want your birthday to be seen on your timeline. Your date of birth is an important piece of personal information for hackers to exploit.
3 Do you mind being tracked by advertisers?
Facebook has eyes across the Web; one study found that its so-called widget — the innocuous blue letter "f" — is integrated into 20 percent of the 10,000 most popular websites. If that is annoying, several tools can help you block trackers. Abine, DisconnectMe and Ghostery offer browser extensions. Once installed on your Web browser, these extensions will tell you how many trackers they have blocked.
Facebook also has a mechanism to show you ads based on the websites you have visited. It works with third-party companies to place cookies on my computer when, for instance, I visit an e-commerce site. That brand knows that I might be looking at girl's dresses. It can ask Facebook to show me an ad for girl's dresses when I log into Facebook. You can control this. Hover over the "X" next to the ad and choose from the drop-down menu: "Hide this ad," you could say. Or hide all ads from this brand. Facebook does not serve the ads itself, so to opt out of certain kinds of targeted ads, you must go to the third party that Facebook works with to show ads based on the websites you have browsed.
4 Whom do you want to befriend?
Now is the time to review whom you count among your Facebook friends. Your boss? Do you really want her to see pictures of you in Las Vegas? How about the woman you met in Lamaze class? Do you want the apps she has installed to know who you are?
Privacyfix.com, a browser extension, shows you how to keep your friends' Facebook applications from sucking you into their orbit. It is preparing to introduce a tool to control what it calls your "exposure" to the Facebook search engine.
Secure.me offers a similar feature. Depending on your privacy settings, that photo-sharing app that your Lamaze compatriot just installed could, in one click, know who you are and have access to all of the photos that you thought you were sharing with "friends."