See the Update below.
President Obama has nearly 19 million Twitter followers, but 70%, or approximately 13 million of them, are fake, according to a new analysis.

Mitt Romney’s Twitter account, meanwhile, has less than 900,000 followers, but only 15% of them, or about 135,000, are fakes.

The numbers come from Fake Follower Check, a tool from social media firm StatusPeople that analyzes a sampling of a Twitter account’s followers and checks for telltale signs of fake followers.

“Fake accounts tend to follow a lot of people but have few followers,” Rob Waller, founder of StatusPeople, told the New York Times in a story about buying and selling Twitter followers. “We then combine that with a few other metrics to confirm the account is fake.”

Analysis of other popular Twitter accounts done using StatusPeople’s tools seems to indicate that the more popular a Twitter account is, the more likely it is that the account will have fake followers — possibly thanks to the work of Internet spammers.

SEE ALSO: Facebook Has 44% Fake Followers; Twitter Has 33%
Fake Twitter followers can be purchased on dozens of websites offering the service for as little as $0.01 per follower. They are sometimes bought by Twitter account managers to give the illusion that a particular brand has more social reach than it actually does.

A sudden spike in Romney’s follower count last month caused speculation that someone was buying fake followers for the account. Both the Romney campaign and the Obama campaign have denied buying Twitter followers. Twitter could not be reached for comment on the matter.

Are you surprised that Obama might have so many fake followers?

Update: As Mashable reader Michael Bauser pointed out in the comments below, the tool works by analyzing up to 1,000 random followers, generating occasionally mixed results. When Bauser used the Fake Follower Check, it told him 31% — or just under 6 million — of Obama’s followers are fake.

“Obviously our scores are more accurate for those with smaller follower bases simply because it would be impossible to crunch all the follower data that Obama has in a reasonable manner via the Twitter API,” wrote StatusPeople’s Rob Waller in an e-mail to Mashable. “We released an update to our tool on Wednesday to make our App more accurate for those with larger follower bases.”