|Telnet is not secure.
Telnet is shipped on most operating systems for backward compatibility, and it should not be used in an untrusted network.
Telnet is a clear-text protocol, meaning that any data transferred, including passwords, can be monitored by anyone else on your network (even if you use a switching router, as switches were designed for performance, not security and can be made to broadcast). Other networks can monitor this information too if the telnet session crosses multiple LANs.
There are also other more active attacks. For example, anyone who can eavesdrop can usually take over your telnet session, using a tool like Hunt or Ettercap.
The standard practice among security-conscious sites is to migrate as rapidly as practical from telnet to Secure Shell (command: ssh). We'd advise you to make this move as soon as possible. Secure shell implementations are available from openssh.org and ssh.com. Most Operating System vendors also distribute a version of secure shell, so check with your vendor first to see if there is a version that has been tested with your OS.
NOTE: Deactivating the telnetd service will not affect your telnet client.|