OnGuardOnline.gov provides practical tips from the federal government and the technology industry to help you be on guard against Internet fraud, securing your computer, and protecting your personal information.

This site describes many things, including how to modify your wireless router security settings to prevent abuse. 

http://www.onguardonline.gov/

Wireless security Items recommended at the web site:

• Use encryption to scramble communications over the network. If you have a choice, Wi-Fi Protected Access (WPA) is stronger than Wired Equivalent Privacy (WEP).  
• Use anti-virus and anti-spyware software, and a firewall.
• Most wireless routers have a mechanism called identifier broadcasting. Turn it off so your computer won't send a signal to any device in the vicinity announcing its presence.
• Change the identifier on your router from the default so a hacker can't use the manufacturer's default identifier to try to access your network.
• Change your router's pre-set password for administration to something only you know. The longer the password, the tougher it is to crack.
• Allow only specific computers to access your wireless network.
• Turn off your wireless network when you know you won't use it.
• Don't assume that public "hot spots" are secure. You may want to assume that other people can access any information you see or send over a public wireless network.