Facebook is the world's largest social network so perhaps it's only natural it would also prove popular with Russians trying to sow discord during the 2016 US election.

The social networking giant was singled out in an indictment unsealed Friday that charged 13 Russian nationals and three Russian groups with interfering with the 2016 presidential election. The 37-page indictment detailed how Russians used stolen identities to pose as Americans on Facebook and Instagram, creating Facebook groups, buying divisive ads and posting inflammatory images.

While not accusing Facebook of any wrongdoing, the indictment detailed how critical the social media platform was to Russian efforts to disrupt the election. Facebook and its photo-sharing app Instagram were mentioned 41 times in the indictment, while Twitter was referred to nine times and YouTube only once.

The world's largest social network, along with Twitter and Google, have been scrutinized in recent months by Congress after US intelligence agencies determined that the Russian government had used these platforms to disseminate false news and advertisements in an attempt to influence US elections in 2016.

It was considered a major security concern during the Senate Intelligence Committee's annual "Worldwide Threats" hearing on Tuesday. The trolls would work both sides of the same issue, with the primary goal to misinform and create political divide.

In an indictment released Friday (PDF), US special counsel Robert Mueller and the Justice Department called out the Internet Research Agency, a group linked to Russian propaganda efforts across social media. Employees for the IRA created troll accounts and used bots to stage arguments and sow political chaos during the 2016 campaign.

The group allegedly controlled the Facebook accounts "Clinton FRAUDation," and "Trumpsters United," and the Twitter account "March for Trump." Many of their tweets would include the hashtags "#Trump2016," "#TrumpTrain," "#MAGA," "#IWontProtectHillary" and "Hillary4Prison," the indictment said.

The agency also set up fake rallies at the same location for both sides of the political divide. On Nov. 12, 2016, the agency organized two events on Facebook, one called "show your support for President-Elect Donald Trump" and one called "Trump is NOT my President." It was at the same time and both in New York.

According to the indictment, the organization included hundreds of staffers dedicated to trolling online and had an annual budget into the millions.

Facebook told the Senate Judiciary Committee in October that about 126 million Americans, or roughly one-third of the nation's population, were exposed to Russian-backed content on Facebook during the 2016 presidential election.

The social-networking giant also said in September it had identified about 500 "inauthentic accounts" that bought $100,000 worth of ads that targeted highly politicized social issues such as immigration, guns and LGBT rights.

Joel Kaplan, Facebook's vice president of global policy, said in a statement that the social network is "grateful" the US government is taking action against the IRA for abusing their services. 

"We know we have more to do to prevent against future attacks. We're making significant investments, including increasing the number of people working on security from 10,000 to 20,000 this year," Kaplan said.

The Smartest Stuff: Innovators are thinking up new ways to make you, and the things around you, smarter.

Special Reports: CNET's in-depth features in one place.