A user recently drew our attention to a problem he was having when using our site with ZoneAlarm. The layout of some pages was changed (eg blocks of text moved down below the fold) when he had Zone Alarm turned on. The pages displayed normally when he turned Zone Alarm off.
On further investigation, it now seems that there are more widespread problems with Zone Alarm. When Ad Blocking is on it seems to randomly block .gifs or jpegs. Randomly in the sense that some gifs/jpegs are displayed whilst others are not.
Does anyone have any ideas on what 'rules' Zone Alarm applies in blocking certain file types?
It depends on how you have it setup. Make sure that "Remove Private Header Information" is not set to ON. That will effect some ads and normal graphics as well.
Generally, Zone Alarm goes after includes in the form of iframes, js inserts (writes), and other multimedia inserts. It also goes after graphics of default sizes (standard banner, skyscrapper, and leaderboard). Finally, it has a load time element based on your connection speed. The idea is to only spend the time dl'ing the ads if you have the bandwidth to spare...