Treasury Department officials were using a secret Gmail back channel to communicate with the Russians at the same time the Kremlin was seeking sensitive financial information on its enemies, including several of Hillary Clinton’s backers, during the 2016 election, according to a report Thursday.

Russia’s financial crimes agency, set up by Russian President Vladimir Putin in 2001, has close ties to the country’s espionage network. It made a request for sensitive documents on Dirk, Edward, and Daniel Ziff, who had run afoul of the Kremlin, BuzzFeed News reported.