The gang, dubbed "Blackjack", which has been tied to the Security Service of Ukraine (SBU), broke into a Russian state firm that works for Tsar Vladimir Putin's army and half-inched 1.2 terabytes of top-secret data.

This data has the maps of more than 500 Russian military bases in Russia and in parts of Ukraine that Putin has nicked. This includes army HQs for the Russian Army, air defence bases, and weapons stores.

GUR said this provided important information about Russian military sites that are done, built, or planned to be made.

As part of Blackjack's cyber attack, all the pinched data was wiped from seven Russian servers. Ukraine's news agency Interfax said the hackers knackered 150 computers.

"Russian builders were left with no data and no copies. They will have to build new sites from memory," sources in Ukraine's cops said.

This comes days after the hacking group was said to have done a cyber attack on the Moscow internet firm M9 Telecom. It left Moscow people with no internet, Ukrinform said at the time.

The paper said an unknown source said it was a practice attack before a bigger one, which would be done to get back at Russian hackers who got into Ukraine's phone giant Kyivstar in 2023.

In that attack, Russian hackers got into the private firm's system from at least May 2023. They wanted to get info and scare them, Illia Vitiuk, the Security Service of Ukraine's (SBU) cyber security boss, told Reuters this month.

Some 24 million users had no service for days starting December 12. In December, Kyivstar, Ukraine's biggest phone firm, said it was hit by a strong attack by hackers that made a "technical problem that made mobile and internet services not work for a bit."

"This attack is a big message, a big warning, not just to Ukraine, but to the whole West to know that no one is safe," Vitiuk said.