Have you ever witnessed your anti-virus program at work?

Last night was a first for me. I was on Youtube listening to music. As soon I clicked on to one song/video, my AVG anti-virus suddenly kicked in and stated it was killing an attempt by The Trojan to invade my computer. I must say I was totally impressed with AVG. This was not a bought version of AVG, it was their free download. I will now purchse the best version available of AVG.

Question: have you ever actually witnessed your anti-virus program at work and attacking a virus?