it doesn't do some sort of ad recognition and block everything. The software uses a list of DNS names or IP addresses to block ads. The people who do the ads are starting to move to different IP addresses to get around AdBlock (or it's just a new server). This is why you have a little tab above the ad to block it, you add that DNS entry to the list. Everytime you see a banner ad just go up and tell it to block, you will never get rid of them all though.