For a few weeks, journalist Mat Honan used every piece of software he could get his hands on to broadcast his location and activities to the world, his friends, and nearby strangers.

To test whether I was being paranoid, I ran a little experiment. On a sunny Saturday, I spotted a woman in Golden Gate Park taking a photo with a 3G iPhone. Because iPhones embed geodata into photos that users upload to Flickr or Picasa, iPhone shots can be automatically placed on a map. At home I searched the Flickr map, and score — a shot from today. I clicked through to the user’s photostream and determined it was the woman I had seen earlier. After adjusting the settings so that only her shots appeared on the map, I saw a cluster of images in one location. Clicking on them revealed photos of an apartment interior — a bedroom, a kitchen, a filthy living room. Now I know where she lives.