NathanE speaks the truth. 
Why on earth aren't you stopping them before they hit the local machine?

Of course AV software isn't useless.
Unless the AV server informs me of a major issue I regularly check the log files over our 150+ workstations and it's amazing just how many viruses/malware are stopped by the AV system..
Why on earth aren't you stopping them before they hit the local machine?