Comment by 8by3

The challenge isn't terribly clever, just some basic crypto maths, same as Anubis. There are a very low number of AI bots that pass it based on my logs, like 0.01% low and I suspect they are interactive agents that bother to run JS as crawlers typically don't. Assuming these are actually run on an end users computers I don't think any amount of cpu/memory weight would be a real blocker. One thing I've seen that is interesting'ish is bots failing as they answer the challenge from a different IP than it was requested from, and the source IP is validated as part of the response so they fail.