You have heard of the dangers of unsecured wi-fi spots by now? You know not to enter your credit-card online when there is no S tacked on the HTTP or no lock to show the site is safe and trusted?
Enter the world of a wi-fi thief, using packet sniffing technologies the data is really just out there floating around. Many years ago, I used a product called Ethereal to open my eyes to the world of network packets, sniffing, and analysis. At the time, I was amazed at how unecrypted and exposed Instant Messages were --
Ten years later, the world is more connected than ever, public-free wifi spots are still common. Just use your brain before entering your important data on the line, or else the wire shark may bite you--
If you have some geeky inclination to inspect the wire and packets of your home network, check out the Wireshark product: http://www.wireshark.org/