According to the Tech Herald newspaper, WiFi networks are very vulnerable to hackers.
Well, we know that already, but the paper refers to an alert issued this month by the FBI saying public that Wi-Fi hotspots in airports, fast food restaurants, book stores, coffee shops, sports bars - you get the picture - are also hacker hotspots.
I think the FBI is quite correct. I've lost count of the number of unencrypted (open) WiFi hotspots I've encountered in my city travels in recent weeks.
Most of them seem to allow access to the Net for a few minutes, then effectively lock you out, after a number of hacker probes are set out - and in my case, are blocked by my paranoid firewall and security software systems. Hehe.
It's getting to the stage that I've given up hunting for freebie WiFi access points and going straight for my 3G broadband dongle - it may be slower than WiFi and have a packet latency of around 300ms, but it works and works securely in most places.
Anyway the FBI has issued a number of guidelines for public WiFi network users, which you can check out here...