Advanced persistent threat definition
An advanced persistent threat (APT) is a cyberattack executed by criminals or nation-states with the intent to steal data or surveil systems over an extended time period. The attacker has a specific target and goal, and has spent time and resources to identify which vulnerabilities they can exploit to gain access, and to design an attack that will likely remain undetected for a long time. That attack often includes the use of custom malware.
The motive for an APT can be either financial gain or political espionage. APTs were originally associated mainly with nation-state actors who wanted to steal government or industrial secrets. Cyber criminals now use APTs to steal data or intellectual property that they can sell or otherwise monetize.