What is a disadvantage of using Telnet?

The correct choice highlights a significant disadvantage of using Telnet, which is the lack of security in its communication. Telnet transmits data in plain text, meaning that any information sent over a Telnet connection, including passwords and sensitive commands, can be easily intercepted by malicious actors. This vulnerability makes it unsuitable for use over untrusted networks, such as the internet, where eavesdropping can occur.

The other options do not accurately reflect the disadvantages of Telnet. For example, stating that Telnet provides encrypted data transfer is misleading, as Telnet by design does not offer encryption. Additionally, while Telnet allows for remote connections, its primary flaw is indeed its lack of security. The requirement for additional authentication is not inherently a disadvantage of Telnet, as many protocols require authentication, but it doesn’t capture the central issue of security. Lastly, while it’s true that Telnet can be used within a local network, this is not a definitive limitation of the protocol itself but rather a matter of best practice regarding its secure use.