[n.s.]

Connecting to the internet wirelessly only makes you slightly less secure than using a wired connection. In many types of networks (like a large ethernet network like you'd find at most offices and in some residential setups), every piece of data that is send out actually goes to every computer on the network, it's just that most machines will ignore data that's not meant for it. With a "packet sniffer" it's trivial to see all the data that everyone is sending around. So having a wired connection does very little to make you more secure.

The good news, though, is that anything important like a bank password is going to use encryption, and the encryption is very, very hard to break. This is true whether the encrypted data is sent wirelessly or not. So going wireless doesn't increase your security risk by any significant amount.

The more common risk for wireless networks that people will find your signal and steal bandwith. This is easy to stop if you password-protect your network, but most people don't bother.