A long-running feud was thrust back into the spotlight today with a contentious report claiming that over half of Facebook's monthly active users are actually fake.

The report, written by Facebook critic Aaron Greenspan, alleges that the social media giant has no way to accurately measure its true user base — or in other words, accounts that are matched up to real people — and that Facebook's reported metrics substantially overestimate the number of real monthly active users.

Notably, Greenspan is a former Harvard classmate of Facebook founder and CEO Mark Zuckerberg. In 2009, Adweek reported Facebook and Greenspan reached a confidential settlement over a trademark dispute regarding the term "the Face Book." Greenspan's new report, however, alleges substantially more than a possibly stolen name.

SEE ALSO: Facebook removes hundreds of fake Russian pages operating in Europe and Asia

"The fact of the matter is that Facebook does not now and will not ever have an accurate way to measure its fake account problem," claims the report. "Taking all of these factors into account, we estimate that 50 percent or more of Facebook’s current MAUs are actually fake."

Facebook vehemently disputes Greenspan's analysis. "This is unequivocally wrong and responsible reporting means reporting facts, even if it’s about fake accounts," wrote a company spokesperson over email.

At least one group appears to be taking the report's allegations seriously, however: Facebook investors. Seeking Alpha, a financial analysis website, notes that Facebook shares fell on Jan. 24 shortly after the Greenspan report was issued.

So, is this report just empty bluster from someone with an axe to grind? Or is there actually something to the claim? The report itself attempts to weigh in on that, with Greenspan writing that "[readers] are accordingly welcome to dismiss this analysis as biased, but should be aware that nonetheless, it may still be correct."

He also writes, because I guess why not throw in a little personal shade while you're tossing around allegations of massive corporate malfeasance, "Mark Zuckerberg is by no objective measure a genius."

Facebook, for its part, has admitted in the past that fake or duplicate accounts exist on its platform. In 2017, the company noted that as many as 270 million accounts could fall into one of those two categories. However, that number is a far cry from what Greenspan claims.

In the end, pinning down the exact number of fake Facebook accounts is likely an impossible task. That doesn't mean accurate estimates don't exist, however. Which just leaves us with the 2-billion-plus user question of whose estimate do you find more believable: Facebook's, or Greenspan's?