WiFi (short for “wireless fidelity,” and sometimes referred to by the technical description “802.11b”) is going places — lots of places. It began life as an alternative to wired Ethernet networks, but it has grown into a tool to expand the boundaries of the Internet. WiFi has allowed an invisible web of wireless networks to creep across the Washington area, offering Internet access to anyone with the right hardware.

The number of locations with WiFi service — or “hot spots” — quadrupled last year, to just under 4,000 nationwide, according to the research firm Instat/MDR.

At home, a WiFi setup can be quite simple. A typical rig consists of a $100-or-less access point, plus under-$50 receivers in each computer. The access point takes a broadband or dial-up Internet connection and shares it with any authorized computer within range.

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