The term wardriving comes from wardialing, which is the random or sequential dialing of phone numbers to find data lines, the numbers of which are logged in order to facilitate future attempts to hack into the computer on the other end. Wardialing was popular in the 1980s, particularly after the release of the movie WarGames, in which Matthew Broderick played a teenage hacker whose wardialing software taps into an experimental defense computer.
While some wardrivers do engage in more malicious hacking endeavors, the average wardriver is typically only searching for open file servers from which to copy software or media files, or looking for free high-speed Internet access while on the road.
Wardriving is frequently pointed out as an example of questionable activity, but it should be noted that, from the point of view of the machines involved, everything is working exactly as designed: a wireless router is advertising its DHCP services over its broadcasting range, and gladly grants access to any portable computer that asks for it. The problem lies in the fact that the wireless protocol has no way of knowing that the request actually came from just beyond the company or residence's borders.
It is possible to lock down a wireless router so that it will not grant access to unknown computers, but this strategy requires a properly organized internal IT service and somewhat reduces the router's ease of use. Many business and residential users alike prefer to leave the router in its default, insecure configuration, because it works for them right out of the box, requiring no special setup.
See also: Warchalking