Are there really 500 million users on Twitter, as the analyst group Semiocast claims? One of the problems of measuring usage on any social media site is that the frequency with which users “use” various different networks tends to fluctuate quite a bit from one person to the next.  Add to that, we have the added problem of whether every “user” is human in the first place.

Semiocast seems pretty confident in their analysis that Twitter has finally broken through the half a billion users barrier however, claiming that the site did so back in June. Of these users, Semiocast says that approximately 140 million of them are located in the United States.

Twitter itself is very guarded when it comes to making any official announcements about user numbers, and with good reason, given the recent controversy of thousands of seemingly ‘fake’ users following politicians Mitt Romney and Louise Mensch. Generally, when Twitter does talk numbers, it only ever refers to ‘active users’ that it can verify.

And so it’s interesting to compare Semiocast’s figures with previous announcements by Twitter; back in September of last year, CEO Dick Costolo proudly announced that Twitter had 100 million active users. More recently, in March 2012, Twitter stated that it currently had 140 million active users.

Obviously, this means there’s a very big discrepancy between Semiocast’s claims and Twitter’s official figures. Given Twitter’s growth rate, it’s highly unlikely that it’s suddenly accumulated 360 million new users in the last few months, which means there’s only one explanation for the difference – there’s a shed load of inactive and fake Twitter accounts out there. Somewhat worryingly, it would seem that they’re in the majority as well.