A top cybersecurity specialist in Russia’s Federal Security Service (FSB) was arrested on Wednesday reportedly on suspicion of leaking information to the U.S. intelligence community — a bombshell accusation that, if true, would mean Washington had a spy in the heart of Russia’s national defense infrastructure.

According to the independent newspaper Novaya Gazeta, the FSB believes Sergei Mikhailov tipped off U.S. officials to information about Vladimir Fomenko and his server rental company “King Servers,” which the American cybersecurity company ThreatConnect identified last September as “an information nexus” that was used by hackers suspected of working for Russian state security in cyberattacks.