Is your Facebook profile under persistent siege? Have you spent hours erasing traces of status updates and wall posts that you definitely didn't post? Then you, like many other Harvard students, have probably had your account hacked using the popular Firesheep tool. This week Facebook began rolling out a new security setting, which, if activated, can protect your account from this type of attack. As this security setting will be released over several weeks, you may be unable to change it now. Check your "Account Security" page intermittently to see if Facebook has made this security setting available to you.