What makes a bot acceptable on Twitter? There are a ton of fascinating Twitter bots, some humorous, some creative, some little experiments, and some impenetrab

What makes a bot acceptable on Twitter? There are a ton of fascinating Twitter bots, some humorous, some creative, some little experiments, and some impenetrable to anyone but the creator. But there are also a lot of spam bots that exist for anti-social causes - to boost a followers count, to spam a product, to (presumably) link to viruses or literal scams. Does anyone know how Twitter decides which bots are unacceptable?