Simple distorted-characters captchas still do a good job of catching unsophisticated bots, which is most of them. They work even better when combined with hidde

Simple distorted-characters captchas still do a good job of catching unsophisticated bots, which is most of them. They work even better when combined with hidden form fields because these bots don't support CSS. Targeted attacks though? You're making your legitimate users suffer only so that you defeat 99% of bots instead of 95%.