Source: Imaginechina Limited via Alamy Stock Photo

Sources reportedly tipped off Ukraine media to a cyberattack launched this week by the Blackjack cyber group, linked to the Security Service of Ukraine (SBU), that they claim was able to "destroy" the servers of Moscow Internet service provider M9 Telecom.

The ISP's website was operational on Jan. 9.

Unnamed sources told state-run Ukrainian media outlet Ukrinform that the cyber operation was in retaliation for the Russia-backed breach of Kyivstar mobile phone operator Dec. 12, which caused communications blackouts across Ukraine. The source reportedly added the M9 Telecom cyberattack was just a "warm up" for more "serious revenge for Kyivstar."

The Blackjack cyber group likewise claimed credit for the late December breach of Moscow's Rosvodokanal water utility, which the group claimed it was able to pull off with the help of the SBU.

Earlier this month, the SBU's cyber chief, Illia Vitiuk, warned that Russia's compromise of Kyivstar, a modern, private company should signal to Western countries that nothing is beyond the reach of sophisticated Russian cyber threats.