To assist with the Senate's investigation into Russia's influence campaign during the 2016 presidential election, Twitter handed over the names of 201 Russia-linked accounts. According to the Associated Press, the accounts are "linked to Russian attempts at influencing the 2016 presidential election."
Twitter provided those names this past week. It hadn't handed them over until then due to legal issues.
Both Twitter and Facebook have confirmed Russia-linked groups utilized their platforms to influence the US public's views during the election cycle. Twitter will testify before the Senate Intelligence Committee on November 1.