What to do:
Only connect to wireless networks you trust. Always use encryption such as https or VPN to view or send confidential material on wireless networks.
Why do it?
Fake access points can be used to steal your information. For example, the free Wifi at a cafe may be operated by an attacker who can see the data of all the users connected to it. The cafe may in fact not offer free WiFi.
If in doubt, do not use.