NoIdea - 11:48 am on Apr 20, 2013 (gmt 0)
Look: if I (server) return to him (a bot) a 403 Forbidden status - this means I admit I've got a hit. Then he (bot) can simply change his weapon (some intruding/spamming kit or simply a proxy.) This means his evolution, and his evolution doesn't bother me:), I'm not interested in it.
I only response with 200, may be send him some irrelevant page (bots can't read I assume:).
But I don't execute any action he requires, alike you do in the case of 403.
Please, help me to understand, which drawbacks are here.