What is "monstermind"

MonsterMind is an alleged US National Security Agency (NSA) program which is an automated response to a foreign cyber-attack.

Revealed by former NSA contractor Edward Snowden, the program watches for unusual Internet traffic patterns that might show an attack. Upon detection, it automatically blocks the traffic from entering the United States.

While similar programs have existed for decades, MonsterMind is unique in that it attacks back, without any human interaction.