In this case, according to the researcher who found the Twitter botnet commands, the botnet itself is an information stealer, most likely aimed at Brazilian banking and financial data.
The point, though, is the ease with which the social network was co-opted as a botnet command and communications network. Again, no big surprise -- the same ease of use and function that attract businesses to Twitter and other social networks as marketing and communications tools make it an effective malware and communications tool.
It's a case of hiding in plain sight and wreaking havoc while hidden there -- although Twitter has restricted the account in question. I find this particularly interesting in light of new figures suggesting that most tweets are meaningless. If Twitterers are already getting a high percentage of blabber that's easy to overlook, it becomes all that much easier to stream crimeware instructions in the current.
Like the crooks' use of url-shorteners we talked about here a few weeks ago, the use of Twitter to control and coordinate a botnet should be a signal to you and any of your employees who tweet to keep your guards up, and raise them a bit higher.