by Jeremy Malcolm, Internet lawyer
Warchalking is the practice of marking chalk symbols on walls of buildings or pavements to indicate that free wireless network access is available in the vicinity. In most cases, the free access is the result of oversight rather than benevolence from the building's occupant!
The legal status of warchalking in Australia is debatable. It is illegal for a person to gain unauthorised access to a computer network. But on one analysis, if a wireless network is left unsecured, it is an open invitation for curious hackers to gain access. On the other hand, is leaving a house unlocked a similar invitation to the curious? Clearly not, so the better point of view is that warchalking should be treated in the same way.
Even if the owner of a wireless network intends to leave it open for warchalkers, legal issues still arise. Their Internet provider will probably prohibit them from resupplying the Internet service to third parties, and will almost certainly make them liable for any damage that these third parties cause. So, if a warchalker hijacks your network for purposes of launching a torrent of spam into the ether, don't be surprised if you find yourself without an Internet connection the next morning.
For those who warchalk other peoples' networks as a hobby, the best advice is to record the open networks if you must, but to avoid gaining further access without permission, and certainly not to attempt to intercept any private communications passing over the network while you are using it.