What law makes it illegal to intercept calls or messages without a warrant?

The Electronic Communications Privacy Act (ECPA) is the correct answer because it specifically addresses the interception of electronic communications, including phone calls and messages. Enacted in 1986, the ECPA was designed to extend government restrictions on wiretaps from telephone calls to include transmissions of electronic data, thereby providing protections for communications that occur over various electronic mediums.

Under this law, it is illegal to intercept, access, or disclose any electronic communications without the consent of at least one party involved in the communication or without obtaining a warrant. This ensures a level of privacy for individuals' communications and sets legal standards for law enforcement and other entities that may seek access to such data.

The other laws, while related to privacy and communications in different capacities, do not directly pertain to the interception of communications in the same legal manner as the ECPA. The Computer Fraud and Abuse Act primarily addresses computer hacking and unauthorized access to computers and networks. The Telephone Consumer Protection Act focuses on telemarketing and restricts unsolicited communications, particularly through automated dialing systems. The Privacy Act of 1974 centers around the protection of personal information held by federal agencies rather than the interception of communications.