There are a few WIFI security protocol standards. The 1st and probably the worst is WEP (Wired Equivalent Privacy), it has the weakest security features and difficult to setup properly. Therefore it is the easiest to hack. If your own network is setup with WEP, then I recommend you use a different protocol. I think it is fine if you are simply browsing for a short period of time. But I would avoid using any WIFI network using WEP for a prolonged period of time (15 - 30 minutes). Never ever transmit confidential information over a WIFI network using WEP. Don't buy anything, don't log into your bank account... nothing.
WPA and WPA2 stands for WIFI Protected Access (version 1 and 2). These are the most secure protocols, WPA2 is more secure. You should setup your own WIFI network using these protocols (WPA2 is preferred). A bit technical, but the main difference between the two is the Advanced Encryption Standard (AES) in WPA2. Security using AES encryption is the official standard used by the US government to encrypt top secret information.
WPS (Wi-Fi Protected Setup) is a more recent security protocol which I just became aware of this week. It is designed to make setting up a secured WIFI network easier. But it turns out that making while making a WIFI network easier to setup, it also makes it less secure. How much less is unknown to me. Is it at least better than WEP? I don't know.
In short, WPA and WPA2 are the way to go. If the WIFI hotspot you are in uses those protocols (especially WPA2), then you should be fine. Can you still get hacked? Yes, theoretically you still can. For the best security you want a direct wired internet connection. It is the absolute most secure way to connect to the internet... but it is still possible to get hacked.
Hotspots using WEP or WPS should be okay for simple browsing. But if you are the overly cautious type, then you will want to simply avoid using any WIFI hotspot that uses those security (or lack thereof) protocols.