The Russian TASS news site was replaced with a message calling on Russians not to let their sons and husbands take part in the Russian invasion of Ukraine on Monday. The Russian Kommersant and Izvestia news sites were also reportedly hacked as well. All three sites were down as of Monday afternoon.
The message featured the logo of the Anonymous hacker group.
"Dear citizens. We urge you to stop this madness, do not send your sons and husbands to certain death," read the message. "Putin makes us lie and puts us in danger. We were isolated from the whole world, they stopped buying oil and gas. In a few years we will live like in North Korea. What is it for us? To put Putin in the textbooks? This is not our war, let's stop it! This message will be deleted, and some of us will be fired or even jailed. But we can't take it anymore."
The message was signed "Caring journalists of Russia."
The message also featured a graphic reading "5,300 Russian soldiers killed in Ukraine in four days. More than in the First Chechen War."
The TASS website was quickly taken down, with visitors receiving an error message saying the site is currently unavailable.
The Russian state-owned news agency RIA Novosti was also experiencing technical difficulties on Monday, with the site in "offline mode" for over an hour.
On Saturday, Ukrainian Vice Prime Minister and Minister of Digital Transformation Mykhailo Fedorov announced the creation of an "IT army" to conduct cyberattacks against Russian targets.
The Ukrainian Center for Countering Disinformation reported on Monday that dozens of websites belonging to Russian and Belarusian public authorities, banks, media and businesses were hit by pro-Ukrainian cyberattacks. The Ukrainian national anthem is also being played on the communication system of Russian troops, according to the center.
The BelZhD's Belarusian railway transport management network has also reportedly been hacked.
Russian government websites including the Kremlin's official site were down for several hours on Friday and inaccessible following reports of cyberattacks on various Russian government and state media.
This is a developing story.