DOJ officials stress that they received approval for the campaign through both a court order and a search warrant.

Joanap and the worm that helps detect vulnerable systems, Brambul, have been around since 2009. However, it wasn't until recently that American officials directly blamed the North Korean government for the attacks, which have targeted the aerospace industry, finance and critical infrastructure. As the DOJ explained, the botnet a threat to national security -- there's a strong incentive to take it down.