US Patent 11399033 Malicious advertisement protection

There is disclosed in one example an advertisement reputation server, including: a hardware platform including a processor and a memory; a network interface; and an advertisement reputation engine including instructions encoded in memory to instruct the processor to: receive via the network interface a plurality of advertisement instances displayed on client devices; extract from the advertisement instances an advertiser identifier; analyze one or more advertisements associated with the advertiser identifier to assign an advertiser reputation; and publish via the network interface advertisement reputation information derived from the reputation for the advertisement identifier.