If Facebook takes security seriously, then it would have avoided McAfee. What a terrible choice. Viruses and trojans run through McAfee like a blowtorch through butter. Even if it catches one, it comes away from the fight with missing limbs and missing key body parts. Avoid at all costs, even if free. The new Norton (since 2009 version) is a far better product and doesn't bog your system down. It's not perfect, but it is the best suite available and by far the easiest to use for the average person. There may be better individual products, but no suite is better at the moment, and at a minimum, every user not part of a competent enterprise network, needs the Big 3 (virus, spyware, software firewall).
I used to hate Norton because it was just as porous as McAfee, but from the 2009 version on, it has overcome all my major gripes. It is the only suite I recommend without any reservations.