The FBI action cut off a massive botnet that was possibly being used for a forthcoming cyberattack aimed at Ukraine.

The FBI admitted that in public speeches and sworn congressional testimony over the last year, it has dramatically overstated the number of encrypted phones it cannot access.

The group took to Twitter: "Law enforcement continues to fail in their hunt for our operation."

Law enforcement in Serbia said a 38-year-old man was arrested in "international operation conducted by the FBI."

House Intel says the FBI didn't adequately engage with hacking victims in the lead-up to the 2016 presidential election.

Baratov is charged with building a for-profit hacking empire whose customers included Russian intelligence.