Wired is most secure because every computer must connect by LAN cable. Wireless networks can be hacked by other wireless devices to achieve internet access and, often, to gain access to other computers on that network. You can set the security on wireless networks through your router. The level of security (WEP/WAP,etc.) is limited to the type(s) the router supports. If you use that, then use the strongest key you can set, and limit the number of connections the router will accept to the number of your networked computers. That will keep your neighbors from using you network to access the internet, but a serious hacker could still figure out how to access your network, if he cared enough.
You can use Shields Up!
to test your network security. It is free and has helped me. If you have never used that site, you will be surprised at your results.