A wireless LAN (WLAN) consists of wireless access points (APs). An AP is simply a modified LAN card with a transceiver and an aerial, rather than a LAN cable. Packets of data are relayed between a physical network server and a wireless device attached to a laptop or handheld device. Data is transmitted using the 802.11(WEP) protocol.

Microsoft Windows doesn't really support the 802.11 protocols. Instead, it relies on driver software that converts 802.11 frames to regular Ethernet before they reach the PC. This is why, before the name Wi-Fi caught on, 802.11b was known as Wireless Ethernet: From the PC's perspective, it is Ethernet.

WEP (Wireless Equivalent Privacy) has the convenience of portability, and the fact that your building does not need to be altered. However security is VERY basic and it can be broken very quickly after gathering 100 MB to 1,000 MB of data using freeware "sniffers" commonly distributed on the Web. Anybody with a wireless PC card and a laptop, can collect enough data in three to thirty hours on a typical wireless network. From that point on, freeware utilities can easily break the WEP code.

Vendors claim that standard transmission ranges are limited to approximately 100ft. In reality the range can be extended to more than to 10 miles (line of sight) using a few pounds of equipment readily available from any electronics retailer. Professional equipment can extend this range even more. If access points are located near windows, a stronger signal will be radiated outside your building making it easier for people to find you.

Here is a site selling some of the antennae that hackers can buy to extend their range. There have also been competitions between hackers to construct aerials from Pringle's cans, and other household items.

Radio signals can easily pass through drywalls with only moderate signal loss(consider what happens when it rains), however solid steel greatly weakens the signal. Water also absorbs a lot of radio signal, this can even include aquariums! Plant foliage (particularly whilst green) and people can severely affect 802.11b performance, therefore having a well planted area around your office could offer some defence. Tinted glass has also been found to effect signal strength much more than clear glass. Wide-open spaces provide the highest level of coverage thus APs should be placed as high-up (the ceiling maybe) to maximise transmission range

This is why "war-chalking" is so popular. A hacker can quite easily sit across the road in their car and access your LAN. This risk can be reduced by increasing the connection speed, which causes the signal to degrade much more rapidly, thus any attacker must be relatively close to your AP(s). Bare in mind that an attacker may not want to steal anything but simply impersonate you, i.e. To discredit etc. If an attacker sends out a defamatory message or virus using your company's identity, you could be left to explain to the authorities. War Chalking has caught the attention of world's intelligence authorities. Rumours abound that the FBI have begun extensive research into the signals that are leaking onto the streets of some US cities.