Facebook has disclosed an estimate of its fake accounts for years, but a closer look raises lots of questions.(New York Times)

Facebook sells advertisers on its access to real people — 2.27 billion of them, a network that exceeds the populations of North America, South America and Africa combined.

But do that many people really use Facebook? The answer lies partly in how many of the accounts are fake.

The Silicon Valley company defines fake accounts as profiles that are either designed to break its rules, for example by spammers or scammers impersonating others, or that are misclassified, such as someone setting up a Facebook profile instead of a Facebook page for a business.

Yet the number of Facebook accounts that fit those descriptions is less clear.

While the company discloses its estimates of fake accounts, its figures have fluctuated and are confusing. Even Facebook admits its understanding of the numbers is tenuous.

“Duplicate and false accounts are very difficult to measure at our scale,” it said in a securities filing in October, and the actual numbers “may vary significantly from our estimates.”

With Facebook reporting a jump in the number of fake accounts on its site this week, let’s dig into what figures it has given before — and why they don’t necessarily add up.

That has implications for the manipulation and abuse of the platform, as well as the company’s business.

A moving target

Facebook’s estimates for fake accounts, made in securities filings, have oscillated.

Facebook cut its estimate of fake accounts significantly in 2016. A year later, it more than quadrupled the estimate. Wednesday, in small print at the bottom of a slide about earnings, Facebook increased the estimate by 36 percent, to 116 million.

Facebook arrives at its estimates by analyzing a sample of accounts, looking “for names that appear to be fake or other behavior that appears inauthentic,” the company said in securities filings. “We apply significant judgment in making this determination.”

Alex Schultz, Facebook’s vice president of analytics, said its fake account estimates fluctuated in part because periodic attacks can cause spikes in the figures. He said Facebook had grown in some emerging markets where fake accounts are more prevalent.

A pile of new fakes

For years, investors, analysts and journalists had only Facebook’s estimates to judge fake accounts. Last year, Facebook introduced a transparency page, which discloses how many fake accounts it has taken down each quarter. Those figures revealed that the scope was far larger than the estimates in securities filings had suggested.

Let’s run through the math. Facebook’s new numbers added up to more than 2.8 billion fake accounts taken down in the 12 months that ended Sept. 30, or about 7.7 million a day.

Facebook previously reported about 3 percent to 4 percent of its active users were fake. According to the new figures, the accounts taken down each quarter were equivalent to 25 percent to 35 percent of its active users (though those accounts were not counted in Facebook’s active-user tallies because they had been removed).

More curious was how Facebook’s estimate of active fake accounts barely budged even as the number of accounts it took down each quarter fluctuated widely.

For instance, Facebook said it had caught 583 million fake accounts in the first quarter of 2018 and 800 million the next quarter. Yet between those two quarters, it told investors its active fake accounts had increased by roughly 1 million.

Those numbers suggest either Facebook happens to be eliminating exactly enough accounts each quarter to keep its active fake-account estimate flat — or its estimate is more like a guess.

“You can use your judgment,” said Brian Wieser, an analyst at Pivotal Research who discovered last year Facebook was claiming it could reach more people in the United States than the Census Bureau said lived in the country. “I think there are reasons to be skeptical of the numbers they put forward.”

Facebook’s figures also imply that over the past year, it has caught and taken down roughly 90 percent of fake accounts that are created on its site — most, it said, “within minutes of registration.” Facebook said it also stopped millions of fake accounts from registering each day.

Schultz said such a success rate was possible because “the vast majority of accounts we take down are from extremely naive adversaries,” who typically create automated accounts that are easy to spot.

Facebook said the vast majority of fake accounts it removed were ones it spotted, rather than ones users reported. Of the 2.8 billion fake accounts it took down in the year that ended Sept. 30, Facebook said, it found 99.3 percent on its own.

Those numbers contradict my experience. Last year, I easily created 11 Facebook accounts that used the same name, occupation and profile photo as my verified account. They remained live for five days, until I reported them to Facebook.

Instagram, which Facebook owns, also left up 10 impostor accounts I created until I reported them; it took down only five, until I alerted a Facebook spokesman.

If an account appears to be impersonating another user but isn’t “engaged in harmful behavior,” Facebook often leaves it up, Schultz said. He said duplicates could be people who lost their password.

Duplicates add confusion

Duplicate accounts are banned under Facebook’s rules. They persist, in even greater numbers than fake accounts, according to the company’s estimates, compounding its problem of inauthentic activity. Facebook’s estimates of duplicates have also seesawed, including nearly doubling in 2017. On Wednesday, Facebook increased its count by 20 percent, to 255 million.

Schultz said Facebook was doing its best to police inauthentic accounts and be transparent. “We disclose it very publicly, in my opinion,” he said.