Blocking is itself a communications channel. You have some data to exfiltrate from extension to server. The page embeds a bunch of URLs to your ad server, you s

Blocking is itself a communications channel. You have some data to exfiltrate from extension to server. The page embeds a bunch of URLs to your ad server, you selectively block based on the data to exfiltrate, the server gets 1 bit per URL. Any additional blocking capabilities (reordering, delaying, selective header stripping) increase the number of bits.