What protocol is known to send complete username and password information in clear text?

The protocol known for sending complete username and password information in clear text is POP3. When using the original version of the Post Office Protocol (POP3), the authentication process does not include any encryption. This means that when a user logs into their email account, their username and password are transmitted as plain text over the network. This lack of encryption makes it vulnerable to interception, allowing attackers to easily capture sensitive credentials if they are monitoring the network traffic.

Other protocols mentioned may also have vulnerabilities, but their contexts are different. For example, IMAP can also transmit credentials in clear text if not secured with encryption, but it primarily manages messages on the server rather than downloading them like POP3. SMTP (Simple Mail Transfer Protocol) is used for sending emails, and while it can also transmit sensitive information without encryption, it is not primarily focused on retrieving user credentials like POP3 does. HTTP is a protocol used for web communication; while it does not secure credentials in transit by default, it is not specifically an email protocol like POP3.

Understanding the implications of these protocols helps highlight the importance of using secure alternatives such as IMAP with SSL/TLS or POP3 with SSL/TLS to mitigate the risk of credential interception.