CNN:

How extensive was Russia’s use of Facebook to meddle with the presidential election? Even Facebook doesn’t know.

One week after it told the country that it had sold $100,000 worth of ads to a Russian troll farm during the 2016 election, Facebook is still not sure whether pro-Kremlin groups may have made other ad buys intended to influence American politics that it simply hasn’t discovered yet, sources with knowledge of the matter said.

These sources said it is entirely possible that unidentified ad buys may still exist on the social media network today.

One issue preventing Facebook from making a full accounting of the problem is that ads are purchased through the company’s self-service tool, which allows buyers to independently purchase and target ads, often without human interaction on Facebook’s side of the transaction