Mark Zuckerberg, Facebook’s chief executive, is testifying before Congress on Tuesday and Wednesday to answer questions about the social network’s failure to protect the data of millions of its users and its role in Russian interference in the 2016 presidential election.

Here are some of Mr. Zuckerberg’s claims, as well as some claims from the lawmakers, which we fact checked. The page will be updated throughout the hearings.

“We made changes in 2014 that would have prevented what happened with Cambridge Analytica from happening today.”

Not quite …

Cambridge Analytica, a political data firm, used information that had been harvested from as many as 87 million Facebook users several years ago to build psychological profiles of voters. Facebook did announce changes in 2014 to limit the access that new apps had to data about its users, but it was not until 2015 that the company rolled out the changes to affect all of the apps on the platform.