you can usually tell a bot or a spammer by the totally unimaginitive and usually computer generated user name...
bots are computer programs sent out into cyberspace...
some of em are malicious spam generators... they'll sign up to a forum and post a pre-determined pile of sh'te, like the rosetta stone crap we got the other week...
a 'CAPTCHA' is that 'type in the letters you see in the picture' thing, bots arent supposed to be able to read it... cos theyre not human, and cant distinguish between characters cos theyre all bent out of shape, you need real intelligence and a mastery of the language to be able to do it i.e. human...