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Why is it that Vista comes with telnet disabled?

If i enable it, is it a potential risk?

Also, in the list there is "telnet client" and "telnet server". I'm wondering what's the difference between enabling each of them?

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Telnet is a protocol that allows one computer to execute a text terminal on another. It's just a connection that transfers text from one to the other computer.

The Telnet server will listen for incoming connections into YOUR COMPUTER. Mostly you will be unaffected since you will likely be behind a little SOHO router, and those don't just let things through like that.

The Telnet client will be installed as a tool for usage in the cmd. If you open the command prompt, you can then type "telnet <server>", replacing <server> with a server name.

Today this is absolutely not used anymore to administer servers and other PCs, since Telnet is insecure. It might be used in very small private networks though.

Telnet is still used on Internet Bulletin Board Systems. These are old forums that are text-only and can only be navigated using the keyboard.

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so are there any free <server> that i could play telnet around with? –  Pacerier Jul 6 '11 at 10:38
    
Theres Bulletin Board Systems that are freely accessible like Synchronet. Try this hostname after the telnet command: vert.synchro.net. You wont find any servers to freely administrate though ;P –  sinni800 Jul 6 '11 at 10:57
    
The telnet client is also useful in case you want to test manually one of the text based protocols like HTTP/POP3/SMTP. –  Robert Jul 6 '11 at 12:54
    
Oh, right, I forgot that, thanks @Robert. –  sinni800 Jul 6 '11 at 13:13
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telnet is not encrypted, your password and all other data will be transmitted as clear text. "telnet server" means, that windows will listen on port 23 for incoming connections allowing users to login (and allowing non-users try to mess with your computer -> potential risk). I'm not sure what "telnet client" means in this context, but i guess the windows firewall will accept outgoing connections on port 23.

Don't use telnet unless you really need to. Use ssh instead (outgoing). For incoming connections see http://en.wikipedia.org/wiki/Comparison_of_SSH_servers

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if i do not do any data transfer, but simply open/enable my telnet client, is it a security risk? (i'm not afraid that people will steal the messages that i've sent.. rather i'm afraid that ppl could use this "backdoor" to whack my com) –  Pacerier Jul 6 '11 at 10:53
    
No, this is not a security risk if you only enable the client. The server though will give you no advantage other than that you can access your cmd (commandline) from outside. And even then, as I said, you won't be able to access it from outside your local network without forwarding ports on your router (if you have one!) –  sinni800 Jul 6 '11 at 10:59
    
Short: yes. Unlikely, but possible. 1) Unsafe passwords ("letmein"), 2) faulty implementation of the telnet server. –  trurl Jul 6 '11 at 11:06
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