There was some recent discussion brought up by Jason Calacanis (@jasoncalacanis) about a sudden spike in some very high profile accounts. Jason determined that this spike occurred on Feb 11. Evan Williams, co-founder of Twitter, refuted the claim by stating that this influx was related to the new "Suggested Users" feature when new accounts are created.
It was pointed out that the spike occurred almost one month after the initial release of the "Suggested Users" feature and shows several graphs from Twitterific on how quickly it happened to several high profile accounts. Some state that there is a spammer creating fake accounts and adding these fake accounts to a circle of users, including the spammer's own account. Again this is just speculation. You can read the entire story with the long list of comments about the report at The Newest Way To Game Twitter - Fake Followers.
Another incident was also reported today from @Minervity. He woke up this morning to find that his account was suspended due to suspicious activity. After an uprising from the Twitterverse his account was restored. Twitter support replied:
"Your account has been restored. It would appear that you have a number of spammers following you and using your material for their own accounts and, as a result, you were caught up in a spam cloud (through no fault of your own) and suspended..."
@Minervity believes that the "spam cloud" is some kind of filter being used to check to see if something was retweeted over and over again.
The post, Twitter Suspended - The Full Story, does not make it clear if these spam accounts were pulling back in his tweets and posted them as their own. If so, it looks like if you get enough of these spam followers you can inadvertently be caught in a spam cloud.
This should be a wake up call for those using the auto-follow feature. Spammers love those accounts. There already has been reports of programs being able to determine which Twitter accounts have this auto-follow feature set up. So you may be prone to get caught up in a spam cloud.