Warchalking Wireless Networks

Are warchalkers identifying your wireless network?

About 20 years ago, attackers used "war dialers" to find computer systems to crack. War-dialer software calls phone numbers looking for answering modems. With the advent of wireless technology, the term "war dialers" morphed into "war drivers," which I discussed in last week's Security UPDATE in conjunction with Science Applications International Corporation's (SAIC's) new wireless honeypot network. The network is designed to trap war drivers—people who drive around with wireless connectivity devices looking for unprotected wireless networks. Intruders then use those unprotected networks to gain free Internet access for various online activities.

This week, I encountered the relatively new trend called "warchalking," which is related to war driving. War drivers use chalk to identify buildings that run wireless networks. According to what I've read, four men sitting at a pizza parlor in London developed warchalking, after at least one of them saw UK Architectural Association students design an office floor plan on the pavement. One of the men mentioned that hobos had once used symbols to pass along useful information, such as identifying houses at which they could get meals. The four men then decided that they could use a similar technique to identify unprotected wireless networks.

Soon thereafter, a Web site appeared where users can log ideas and share information, and the idea has taken off like a Colorado wildfire. As far as I know, three basic symbols are in use, and you can download a PDF file of the symbols. The first symbol, two halves of circle joined back to back at the curved edges, represents completely open wireless nodes. The second symbol, a circle, represents a closed node. The third symbol, a circle with the letter "W" in the center, represents a Wired Equivalent Privacy (WEP) node that probably won't allow easy public access. In addition, each symbol might have a Service Set Identifier (SSID) indicated above it, which tells people how to access that particular wireless node. To obtain SSIDs, intruders use sniffer software that can crack wireless LAN codes.

Using chalk to identify available wireless connectivity points might seem somewhat useless at first: Someone can rub off the chalk and it washes away in the rain. But chalk is less intrusive and less damaging than other media such as spray paint. In addition, any given wireless network might change its configuration over time—and warchalkers can easily adjust symbols accordingly.

Some wireless network operators have complained in online public forms about having warchalkers mark their networks. However, because the symbols are visible, network operators know that others have identified their premises as having wireless networks. Those operators can decide whether and how they want to react to the situation. If operators don't want unknown persons connecting to their network, they can apply various forms of security to prevent such access. Some operators think warchalking is a good idea and plan to print the relevant symbol on paper and put it in their building windows. Others propose adding symbols to identify networks that are voluntarily open to the public as a means to share unused bandwidth.

All in all, warchalking is a relative invasion of privacy that heightens the security risks and liabilities involved with maintaining a network. However, as wireless nodes become more commonplace, warchalking will probably disappear.