Mitt Romney recently piled up tens of thousands of new Twitter followers. His roster of fans on the microblogging site is growing so fast, in fact, that suspicious liberal critics are speculating that the GOP presidential candidate's campaign must be buying phony followers to make it look like his popularity is exploding. What's behind Romney's sudden Twitter surge? Here, a brief guide:

Just how fast is Romney gaining followers?

Before this past weekend, Romney had been picking up followers at a steady, if modest, clip — a rate of 5,000 or 6,000 a day. Then, on Friday, something changed, and suddenly he was adding 1,000 to 4,000 fans an hour. He picked up 23,926 on Friday, 93,054 on Saturday, and 24,285 on Sunday, according to the website 140Elect, which first reported the spike. 140Elect's graph illustrating the explosion, says Charles Johnson at Little Green Footballs, "looks like a hockey stick."

What happened?

That's the big question. The simplest explanation, Johnson says, is that Team Romney bought fake followers to create the illusion of skyrocketing popularity. It wouldn't be the first instance of such tactics being used in high-stakes politics: A year ago, Newt Gingrich, then seeking the Republican presidential nomination with little momentum, boasted 1.3 million Twitter followers — twice as many as Sarah Palin had. Internet search engine firm PeekYou looked into the matter, however, and concluded that 92 percent of Gingrich’s followers were fake. (As part of its Gingrich investigation, PeekYou bought some followers on eBay to prove it could be done.) A former Gingrich staffer admitted the campaign had bought phony followers.

Why assume that many of Romney's new followers are fake?

His other metrics, including mentions and retweets, stayed consistent or even trended downward while his list of followers ballooned. Many of the newcomers have names that look like random assortments of syllables, and have few, if any, of their own followers. While most Twitter users have followers who aren't real people, the fakes are usually creations of spambots looking to hook unsuspecting people on some scam. PeekYou has estimated that only 20 percent to 30 percent of other politicians' followers are "real," compared to 35 percent to 60 percent for the average Twitter user.

Did Romney buy followers?

Despite what several liberal bloggers say, Romney's campaign states emphatically that he did not. "We have reached out to Twitter to find out additional information regarding the rapid growth," Zac Moffatt, the Romney campaign's digital director, tells Buzzfeed. Meanwhile, Zach Green at 140Elect is giving Romney the benefit of the doubt: "Personally, I think this is too obvious for the Romney campaign to have done. It's more likely somebody is trying to plant a story to embarrass him." One thing is certain: Romney could use a boost to catch up with President Obama on Twitter. Even after his recent surge, Romney has just 816,680 followers as of early Monday. Obama had nearly 17 million more.

Sources: 140Elect, Buzzfeed, Little Green Footballs, TIME