A person who uses his expertise to gain access to other people's computers to get information illegally or to cause damage, is a

Correct option is A

Correct Option – (a)
Introduction: Cybersecurity terminology defines individuals based on their actions and intent when interacting with computer systems.
Information Booster:
· A  hacker, in the common and often negative sense used in media and law, is precisely defined as an individual who uses their  technical expertise and knowledge of computer systems to  gain unauthorized access to data, networks, or devices.
· The motives can include  stealing sensitive information (illegally obtaining data), causing damage (e.g., deploying viruses, ransomware), or disruption.
· The definition in the question captures the core elements:  use of expertise, unauthorized access, and illegal or harmful intent.
Additional Knowledge:
· Analyst: A professional who examines data or systems to understand them, typically in a lawful and authorized capacity (e.g., systems analyst, intelligence analyst).
· Messenger: A generic term for someone who delivers a message; in computing, it could refer to a communication app or service, not a person with malicious intent.
· Spammer: An individual or entity that sends  unsolicited bulk messages (spam), primarily for advertising. While unethical and a nuisance, spamming does not necessarily involve the technical exploitation to  gain access to a system; it often involves misuse of legitimate email services or purchased lists.