From the git repo: > Blocking known bots and crawlers Currently, the User-Agent string is often used as a brute-force way to block known bots and crawlers. The

From the git repo: > Blocking known bots and crawlers Currently, the User-Agent string is often used as a brute-force way to block known bots and crawlers. There's a concern that moving "normal" traffic to expose less entropy by default will also make it easier for bots to hide in the crowd. While there's some truth to that, that's not enough reason for making the crowd be more personally identifiable. This means that consumers of the Google Ad stream have one less tool to identify bots, and will pay Google for more synthetic traffic, impressions and clicks; this could be a huge revenue boost for Google. A considerable amount of their traffic is synthetic. I doubt this was overlooked.