Hot on the heels of ‘war driving' (see Dangerous driving , May 2001) comes ‘war chalking', the digital equivalent of the bush telegraph for hackers looking for unprotected wireless Internet access.

Wireless networks are almost too easy to access – and therefore extremely vulnerable to abuse. Since there are no wires involved, hackers do not need physical connections to the network for their computers to tap into it and access systems residing behind the firewall.

War chalking is a code developed to advertise the presence of wireless networks. Scrawled in chalk on pavements, walls or other objects, a so-called ‘war chalk' uses a set of symbols to alert wireless users to the location, speed, network name, security and type of a network nearby.

Our hypothetical example (see right), shows the war chalking symbol for an open network called ‘infoconomy', that uses the 802.11b protocol running and offering 11 megabits per second bandwidth, located at a distance of 25 metres to the right of the symbols. It also provides a web site address where users can obtain more information about who is running the network.

Hackers are not the only ones responsible for war chalk. Some altruistic companies have deliberately configured wireless networks to be open to offer broadband Internet access to anyone who needs it.

One of the inventors of war chalking, web designer Matt Jones, says that it is "being recognised for the public good" it provides. But while it has become an almost universal language for hackers, there are already problems with translation: French hackers have created their own language and are refusing to adopt the English symbols. But if a company has a wireless network and IT staff have suddenly noticed strange signs outside on the pavement, it might be time to tighten security…