Comment by Sohcahtoa82

I've seen sites that use unexpected HTTP response codes, I think to try to defeat bots. The front page would return a 503 Service Unavailable, but the body was just normal content that would load a bot detection script and then redirect you to the actual content.

I successfully wrote a bot that would bypass it all, but it was weird, and became a slight challenge since I couldn't rely on response codes to determine if I succeeded. When I solved the challenge, it would return a 400 Bad Request while serving me the content I was looking for.