A Facebook official told CBS News's Jeff Pegues Thursday that the company's investigation into Russian-linked internet trolls is far from over.

"We have not closed the book on this," the source said, adding that the numbers released Wednesday could go up.

In a blog post published Wednesday, Facebook's Chief Security Officer Alex Stamos said, "We have found approximately $100,000 in ad spending from June of 2015 to May of 2017 — associated with roughly 3,000 ads — that was connected to about 470 inauthentic accounts and Pages in violation of our policies."

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The company's information security team is looking into the ads. A source says Facebook has been aware of this type of information influence operation for years, telling Pegues, "If you look at these types of activities, they ebb and flow," depending on the election season.

Facebook officials have confirmed that some of the activity has been traced to a group called the Internet Research Agency which is a company based in Russia. The entity was started by a man with ties to Russian President Vladimir Putin. IRA – as it is called – has a well-documented history of employing hundreds of "trolls" to stir up divisions on the internet. It carries a pro-Kremlin message and anti-Western rhetoric.

Facebook officials insist that they cannot say for certain whether most of the information in the ads favored Donald Trump's presidential candidacy. A source familiar with the Facebook investigation told Pegues, "It just wasn't cut and dry."