Dear PropellerHeads: I'm no privacy nut, but I get a little uneasy when Web ads invite me to "Click here to find singles in Richmond, Va." How do they know where I am?

A: I'd be more concerned about how they knew you were single! Maybe they took control of your webcam and figured anyone who combs his hair like that must live alone? OK, calm down: the Internet is still the place where "nobody knows you're a dog," as they used to say.

For now your marital status is somewhat safe, but it's open season on your whereabouts. On the Internet right now it's all about location, location, location.

Your ad probably used "IP geolocation" to determine where you were. Internet connections are assigned "Internet Protocol" addresses, which are sets of numbers separated by periods, like "99.18.50.219" (see whatismyip.com for yours).

Internet providers allocate ranges of IP addresses to different localities. Companies like MaxMind (maxmind.com) sell databases of IP-to-location mappings. Punch your IP into http://bit.ly/cFXn2r to see where they think you are.

IP geolocation is only accurate to the city at best. It's good enough for cyber-personals, but insufficient for turn-by-turn directions, "hyper-local advertising," and alerting you when your buddies are nearby.

These are some of the uses envisioned by the World Wide Web Consortium (w3c.org), which added geolocation capabilities to HTML5, the upcoming version of the computer language used in Web pages. The Big Five browsers - Internet Explorer, Firefox, Opera, Google Chrome and Apple's Safari - have added support for location awareness to their most recent products, while Loki (loki.com) plugs into older browsers to "location-enable" them.

How do they find you more accurately than IP geolocation? For some phones, they use the built-in GPS chips. For other phones and laptop or desktop computers, they gather information about nearby cell towers and Wi-Fi networks.

When the PropellerHeads at Data Directions aren't busy with their IT projects, they love to answer questions on business or consumer technology. Email them to questions@askthepropellerheads.com or contact us at Data Directions Inc., 8510 Bell Creek Road, Mechanicsville, VA 23116. Visit our website at www.askthepropellerheads.com.