The protocol used for secure communications over a computer network is called Secure Sockets Layer (SSL) or its successor, Transport Layer Security (TLS). These protocols encrypt data transiting between a client and a server, ensuring confidentiality and integrity during transmission. SSL/TLS is essential for secure online transactions, protecting sensitive information such as credit card numbers and personal data. It is commonly employed in web browsing, email, and other forms of communication to safeguard against eavesdropping and tampering.