Threat actor / Advanced Persistent Threat (APT)

A threat actor is any individual or group responsible for a cybersecurity incident. An Advanced Persistent Threat (APT) is a specific, more capable category of threat actor: one with significant expertise and resources that pursues its objectives over an extended period, adapting its methods to get around defenses rather than giving up after being blocked once. APTs, often linked to nation-states, are a particular concern for critical infrastructure because of their patience and resourcing relative to opportunistic attackers.