A new study from security firm Barracuda Labs provides some interesting insights into the state of the Twitterverse. Unfortunately for the microblogging startup, the stats say that most of its users aren’t very active.

The study looked at around 19 million Twitter accounts (PDF) in order to figure out how people are using Twitter (). It started with one assumption: an active or “True” Twitter user has at least 10 followers, follows at least 10 people, and had tweeted at least 10 times. By that definition though, only 21% of Twitter users are active users.

There’s a great deal of interesting data in the breakdown. Only 26% of Twitter users had 10 followers or more by December 2009, while only 40% were following 10 people or more (in fact, a majority of Twitter users, 51%, were following less than five people).