Facebook Inc is buying a software firm that specializes in authenticating government-issued identification cards, the two companies said on Tuesday, a step that may help the social media company learn more about the people who buy ads on its network.

U.S. lawmakers have expressed alarm at Facebook's limited ability to know who is buying advertisements, including election-related ads, on the world's largest social network.

Boston-based Confirm Inc, which is privately held, said on its website that the acquisition was the culmination of three years of work to build technology to keep people safe online.

Facebook said in a statement Confirm's "technology and expertise will support our ongoing efforts to keep our community safe."

Terms of the deal and how Facebook would apply Confirm's software were not revealed.

Confirm will wind down its operations and its employees will join Facebook in Boston, a person familiar with the acquisition told Reuters.

Confirm's website listed 26 employees earlier this month, according to a version archived by the Google search engine. It says on its website that it has more than 750 clients.

Last year, Facebook said that suspected Russian agents had been paying to boost Facebook posts in the United States in an attempt to divide the electorate around the 2016 presidential election. Moscow denies the allegations.

The company later said it would begin requiring organizations running election-related ads to confirm their identities.

Facebook has more than 6 million different advertisers, and buying ads has historically required little more than a Facebook page and a credit card.

Confirm says that its software allows for proof of identity for online transactions, allowing users to detect potentially fraudulent activity.

Moelis & Co and Goodwin Procter advised Confirm on the transaction. Hogan Lovells advised Facebook.