Most of the utilities we use to log into servers these days like Telnet, FTP, and Email, send the login and password text unencrypted. Anyone who can intercept your network traffic will learn your logins. And if you login as root, your system will be owned. It's bad enough if you're on a wired network, as anyone who has worked next to Kevin Rose will attest, but the risk is multiplied 1000 fold on a wireless network. And idiot can capture Wi-Fi traffic, even if WEP encryption is turned on. The only truly secure way to use Wi-Fi is to encrypt the traffic end to end using a good scheme like VPN or... SSH!
Start by replacing Telnet with SSH. Instead of running the telnet daemon on the server side, you'll have to run SSHd. And you'll need a new client. Free implementations of SSH client and servers are available for all platforms. Some, like Linux and Mac OS X come with SSH. Most recent versions don't even turn on telnet - it's that dangerous.
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