The option will exist as part of our advanced security features, which you can find in the "Account Security" section of the Account Settings page. But you have to go out of your way to enable this protection, and you might have to wait. Facebook has at long last offered an option to use the encrypted "HTTPS" protocol, a feature it will begin rolling out today but won't finish for a "few weeks." Facebook seems to recognize this, writing, "We hope to offer HTTPS as a default whenever you are using Facebook sometime in the future."
– Facebook has begun rolling out an important new protection, and Gawker's Ryan Tate says users should "jump on this" as soon they can. It's an encryption tool called Facebook HTTPS that will "keep any random jerk in the café from hijacking your account." Unfortunately, users have to opt-in to the service, at least for now, and Tate offers a walk-through of how to do it under Account Settings. (Facebook does, too, in its blog post.) You may not be able to make the switch immediately, but keep checking back. "Switching to HTTPS is important because a browser extension called Firesheep has made it especially easy for anyone sharing your open wireless network—at cafe or conference, for example—to sniff your credentials and freely access your account," writes Tate. Also note that this protection doesn't apply to the Facebook iPhone app.