You may see someone driving slowly around your home, office building, or public parks with a small netbook or IPAD computer and a directional antenna. The directional antenna may look like a coffee can or tennis ball can with a wire to the IPAD, laptop, or netbook. The purpose of this activity is to find open networks that they can use to view websites or exchange files.
The problem is if they exchange child pornography which is illegal and is traced back to your home, business, or organization's router. Once a wireless network that is accessible is located, the site may be marked for others to use with a coding schema known as warchalking. Warchalking symbols are explained on this site http://www.guide-to-symbols.com/warchalking/ . There is a book called, "Scene of the Cybercrime" by Debra Littlejohn Shinder and Ed Tittel from Syngress Books that discusses Wardriving in some depth . There is another online source who also discusses it . There is also an interesting video on Youtube about the subject where two women in the U.K. explain it .
It is important to secure your router and not have open access networks. Most of the trouble can be avoided by changing the default password for access to something difficult. The second thing you can do to improve security is to disable remote configuration and enable strong encryption such as TKIP-AES. Lastly, you can use MAC filtering so that only transactions from your computers or your organization's computers are accepted. Many of these concepts are illustrated with pictures and discussed in depth in the Linksys networking book .
Shinder, D., Tittel, E., (2002), "Scene of the Cybercrime," Syngress Books, ISBN 1-913836-65-5