If you are still using Telnet for for connecting your PC to a server on the network then you should disable it and should be replaced it with SSH. There is high security risk if you are using Telnet for accessing server as Telnet sends clear text passwords and usernames through logins which can be hacked by anyone.
For some reason few hosting service provider don’t disable telnet by default thus you need to make sure you have disable it for your server. TELNET server listens for incoming messages on port 23, and sends outgoing messages to port 23 thus you will have to close port 23 and will have to turn off Telnet.
How to Disable Telnet service for your server.
1. Login to your server through SSH and su to root.
2. Type pico /etc/xinetd.d/telnet
3. Search line: disable = no in above file and replace No with yes ie disable = yes
4. Now restart the inetd service: /etc/rc.d/init.d/xinetd restart
5. Make sure you have to turn it off through chkconfig as well, because you can still start Telnet through it.
/sbin/chkconfig telnet off
6. Lastly you need to scan your server to ensure port 23 is closed.
nmap -sT -O localhost
Also run ps -aux | grep telnet and if you find anything other than “grep telnet” as result kill the process.
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