Security alert! Joining open public wireless hotspots is a bad idea for your data security. A really bad idea.
When you join an open Wi-Fi network, your data is sent through the air in a way that is very easy for anyone else on that network to sniff out, steal and even take control of. A quick read about Firesheep should get your spider sense tingling.
If public Wi-Fi is something you really like using, then there are services that can hide your data and keep you safe. One we've looked at is called Cloak, and it's now available on Mac and iOS, with Windows and Android versions coming soon. It's a virtual private network (VPN) service that cleverly works on a data-limit basis. It's free for up to 1GB of usage per month, or you can pay to get more.
Simply put, either stop using open Wi-Fi, or grab a tool like Cloak to keep your data safe.