On Friday night, the Jester gained access to the Russian government ministry's website, according to CNN. And he left a message: Stop attacking Americans.
"Comrades! We interrupt regular scheduled Russian Foreign Affairs Website programming to bring you the following important message," he wrote. "Knock it off. You may be able to push around nations around you, but this is America. Nobody is impressed."
His hacking of the website included subjecting visitors to the ear-piercing sound of an American civil alert message -- that shrieking dial tone that accompanies emergency weather broadcasts.
The U.S. government recently blamed Russia for meddling in American politics. Russian intelligence agencies have been accused of hacking into Democratic National Committee emails and the sites of other Democratic Party-linked organizations, leaking damning information to sway the election away from Hillary Clinton.
Read alsoReuters: Democratic Party says it was hacked again, blames RussiansStolen emails have been taken by Russia and published by WikiLeaks.
Russia and President Vladimir Putin have denied involvement.
The Jester referenced Putin's denial in his webpage graffiti.
Read alsoU.S. accuses Russia of directing cyberattacks to 'interfere' with elections"Let's get real, I know it's you, even if by-proxy, and you know it's you," he wrote. "Now, get to your room. Before I lose my temper."
In the past, Jester has taken down jihadist websites, hacking into communication forums, and identifying potential terrorist threats. Ex-FBI agents have called him "the Batman of the internet."
Read alsoCzech police arrest Russian in connection with U.S. hacking attacksIn an exclusive interview with CNNMoney this weekend, Jester said he chose to attack Russia out of frustration for the massive DNS cyberattack that knocked out a portion of the internet in the United States on Friday.