What do you call a person who gains unauthorized access to a computer or network?

A person who gains unauthorized access to a computer or network is referred to as a hacker. The term "hacker" has evolved over time, and while it can sometimes carry a negative connotation, it primarily denotes someone who uses technical skills to explore and manipulate computer systems. This can include both ethical hackers, who test security systems to identify vulnerabilities, and malicious hackers, who exploit systems for personal gain or to cause harm.

The other options do not fit the definition as clearly. A coder is typically someone who writes computer code, an administrator is a person responsible for managing the day-to-day operations of a computer system or network, and a user is anyone who interacts with a computer or network but does not necessarily have advanced technical skills or authority. Thus, "hacker" is the most accurate term for someone who gains unauthorized access.