The trend is called war chalking. (It derives its name from the now-ancient practice of war dialing, in which hackers would set their modems to dial every telephone number in town, in search of other modem-connected computers.) Nowadays, some ingenious mobile hackers do a war drive through cities, mapping any wireless network they find as they cruise past at 35 miles per hour. Some return to war-chalk the locations with the best networks.
At last summer's DefCon hacker conference in Las Vegas, I rode along with a team in the first-ever war-driving contest. More than 80 contestants raced through town for 2 hours, waving antennas out the windows of their cars. The team I observed found more than 200 wireless access points that had either no security or limited security within a 9-mile radius from our starting point just off the Strip. And the winning team found more than 500 vulnerable access points in the same amount of time.
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