People tend to rely on wireless networks a lot these days, but there are things concerning the security measures employed in this method of connectivity that people don't know about, thus putting themselves in danger of being spied on.
It should first be noted, that wireless networks are less safe due to their nature: to spy on a wired network requires physical access to the cables, whereas spying on a wireless network can be done using the right radio. To further make matters worse, the security protocol used in most public hotspots, WEP (wired equivalent privacy), fails to disallow anyone with the right software tools from listening in on network traffic using an ordinary computer. While this issue is being taken care of by spreading the use of the newer security protocol – Wi-Fi protected access – it is still not present in most public hotspots.
The real danger while using these open networks isn't the possibility of being spied on in detail (it would require a lot of work to do so and is therefore not something to worry about), but the fact that stealing usernames and passwords is generally very easy.
All is not lost, however, since most of the confidential transactions will go through a secure server (most banks, for example, use a secure server). Secure servers encrypt information from end to end, meaning that anyone who intercepts the transaction will only see gibberish. To be sure whether you are using a secure server, you can check the address in the address bar: it will start with “https://” as opposed to the usual “http://” if the server is secure.
It is recommended not to send sensitive information via email, because in most cases emails are not encrypted.
Your internet browser should be up-to-date at all times in order to prevent security hole exploits.