Abstract: Systems and methods are provided that discover undesired advertisements on publisher web pages and automatically block advertisers or advertising channels associated with the placement of those advertisements from placing advertisements on the publisher web pages. An advertisement discovery and blocking system may discover advertisements on a particular publisher web page and placement pathways associated with those discovered advertisements. The system may then compare the discovered advertisements and placement pathways with a set of rules in an advertiser rule list. The system may detect advertisement violations based on the comparison of the set of rules in the advertiser rule list with the discovered advertisements and placement pathways. The system may add advertisers and advertising channels associated with the detected advertisement violations to a list of blocked advertisers. The list of blocked advertisers may be provided to the publishers and the advertising channels.