Which protocol is primarily used for secure data transmission over the Internet?

The protocol primarily used for secure data transmission over the Internet is HTTPS. HTTPS stands for HyperText Transfer Protocol Secure, and it allows for encrypted communication between a user's web browser and a web server. This encryption is achieved through the use of TLS (Transport Layer Security) or its predecessor, SSL (Secure Sockets Layer), which ensures that any data transferred remains confidential and is protected from eavesdropping or tampering by third parties.

In contrast, protocols like FTP (File Transfer Protocol) and HTTP (HyperText Transfer Protocol) do not incorporate encryption by default, making data sent over these protocols susceptible to interception. SMTP (Simple Mail Transfer Protocol) is primarily used for sending emails and does not inherently provide secure transmission either, although it can be secured through additional mechanisms like SMTPS. Therefore, HTTPS is the correct choice for ensuring secure data transmission on the Internet.