Using public WiFi is becoming risky, if you pass important information insecurely over it. There are freely available tools out there that will listen in to all the network traffic, looking for passwords — and now there are tools, like Firesheep, mentioned below, that will hijack sessions you’ve already securely logged into.
Takeaway lesson? Any time you’re using a public WiFi spot, encrypt all activities if you can. And definitely encrypt passwords going to your mail server. I’ll be enforcing that last one on my mail server in the next few days.
(from Ars Technica)