Notice some suspicious activity on your wall? Well there some simple security settings built into Facebook – some of these settings are new while others have been around for some time – that should help you quickly detect if any other person is secretly logging into and using your Facebook account.
If you come across an unknown device / location in the list, say you are Mac user and the device listed is IE on Windows, just click the corresponding “end activity” link and it should immediately log you out from that machine.
For extra safety, you may also choose to receive email and SMS alerts if someone else tries to log into your Facebook account from a previously unknown computer or mobile phone. (I wish Google could bring such a feature to Gmail as well).