You should really block the advertising category with your URL filter. Why? Because hackers are flocking to the AD networks to infect machines. They are exploiting a weakness where major online sites such as newspapers are not scanning ads. These malicious Ads go into the websites rotation and can be there for weeks without being discovered. Recently Yahoo had an ad that was displayed for over a week that was infecting European users. It might make web pages look a bit funny to have Ads blocked, but you will save yourself from having to fight malware protection. If you need a recommendation on a good firewall that will stop malicious Ads, contact me at 262-373-9070 or james@tbjconsulting.com