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Stuck behind a dial-up connection in 1999, Sanjay Parekh grew frustrated having to enter information like his city and state before he cold find store locations on, say, the Federal Express and Ikea Web sites. "These sites should already know where I am," he thought. Rather than curse at his monitor, he formed Digital Envoy in Norcross, GA, to make his idea real. Four years later his product, NetAculty, is used by eBay, AOL Time Warner, Microsoft, and others to determine a visitor's locality. It traces connections back thorough Internet switching stations to the network nodes where log-ons originate- almost always in a visitor's city or town. This is close enough to give users local weather forecasts, or the addresses of nearby electronics stores, without their having to enter any data. NetAcuity also enables Web sites to automatically tailor advertisements. A billboard ad for Home Depot, for example, could announce a sale at a store near the visitor's home. Indeed, Google uses NetAcuity to target area-specific ads. "A lot of people don't know about us," Parekh says, "but everyone is touched by us,"