For years, a small and disparate Ukrainian team including IT experts, intelligence officers and a criminal prosecutor has kept a wary eye on a group of hackers nicknamed Armageddon.

The hackers were based in Crimea, shielded by the Russian government, which had seized the region in 2014, and out of the reach of the Security Service of Ukraine.

The Ukrainian team watched Armageddon from afar to learn the ways of its enemy. It quietly studied the hacking group’s cyber weapons, intercepted phone calls and even outed its purported leaders.