Among international computer hackers, he was known simply as “Kolypto.”

In real life, he was Mark Vartanyan, a Russian national labeled by the FBI as “a key resource” for the cyber underworld.

Federal prosecutors in Atlanta say Vartanyan developed, improved, and distributed a pernicious computer malware toolkit known as Citadel that targeted major financial and government institutions around the world. Federal prosecutors say the malware, designed to steal financial account credentials and personally identifying information from computer networks it infiltrated, infected an estimated 11 million devices and resulted in more than $500 million in financial losses.