Facebook.com loads up on a computer screen | Loic Venance/AFP via Getty Images Facebook: Russia ads seen by 10 million people Because Facebook’s ad system only presents ads to users when they cross a minimum standard of relevance, about a quarter of the ads were never seen, company said.

Facebook on Monday said 10 million people saw ads placed by Russia's Internet Research Agency that the company shared with congressional investigators Monday. The cache, targeted at 2016 U.S. presidential election voters, includes paid spots "focused on divisive social and political messages across the ideological spectrum" on topics like LGBT issues and immigration, the company said.

That information came in a blog post from Elliot Schrage, Facebook's vice president of policy and communications. According to Schrage, many of the ads cost little. "For 50% of the ads, less than $3 was spent; for 99% of the ads, less than $1,000 was spent," Schrage wrote. And because Facebook's ad system only presents ads to users when they cross a minimum standard of relevance, about a quarter of the ads were never seen, he added. Moreover, only about half of the advertisements in question ran before election day.

While the ads at issue were paid for in rubles, "currency alone isn't a good way of identifying suspicious activity, because the overwhelming majority of advertisers who pay in Russian currency, like the overwhelming majority of people who access Facebook from Russia, aren't doing anything wrong," Schrage wrote.

Schrage also noted that the batch of ads would have violated Facebook's policies even if they had been placed by Americans because they were part of "a coordinated, inauthentic operation." Facebook didn't share images or specific examples of any of the ads it sent to congressional investigators.