Microsoft warns Sandworm could be gearing up for more attacks in Ukraine

Microsoft calls the group Iridium, but it is perhaps best known as Sandworm.

It has been accused of attacks on Ukraine's electric power grid and government agencies.

Sandworm is tied to Russia's military intelligence agency GRU, the software company says.

Ukraine's defenses have largely fended off a major cyberwar with the help of foreign tech companies including Microsoft.