Andrew Hickey, 10, and his sister Sarah, 7, unearth a cache as they go geocaching in Silver Spring, Md., in June 2006. (Michael Temchine/For The Washington Post)

Three hours later, it became clear the suspicious man and bomb scare were nothing but a hobbyist taking part in a global scavenger hunt that had been going on for years.

I was first introduced to the scavenger hunt on a particularly hot summer day as a teenager. My sister and I spent hours traipsing through a mosquito-filled graveyard near Bar Harbor, Maine, forced by our parents to engage in an activity called letterboxing. “It’s a treasure hunt,” they entreated. “It’s fun.”

Letterboxing is a scavenger hunt in which you follow clues in order to find small, weatherproof boxes in areas like parks, forests, or graveyards. When my sister and I finally found the box that day, we were disappointed to open it and find nothing but a stamp and book waiting for us inside. The stamp was to be proof for our own logbook that we had found what we were looking for.

But after several days spent tracking containers left behind by other hide and seekers around Maine, we looked proudly at our logbook now filled with stamps, looking very much like the passport of a world traveler.

Letterboxing has now been taken to a whole new level with the increasing popularity of Geocaching, a high-tech version of the worldwide treasure hunt. The small, waterproof containers are now called “geocaches” or “caches”and hide-and-seekers can now use Global Positioning Systems (GPS) or other technology to find the containers and record their findings. Instead of noting who came before you by reading a list in a book left inside the container, like names on a library card, hide and seekers now share their experiences online.

The bomb scare in Britain can be blamed on a man who just wanted to geocache, placing his plastic container under a flowerpot.

He’s one of five million geocachers in more than 100 countries worldwide, on all seven continents. (I’d love to know who braved Antarctica.) At any time, up 10,000 gamers are on the quest.

If you want to join the millions of geocachers, you can learn how to play the game and participate at this Geocaching Web site, buy a GPS through Garmin, or get a navigator on your cell phone here. But for those who still want to kick it old school, visit my favorite home for letterboxing. Just don’t hide your container under a flowerpot. I suggest the forests of Maryland, where the Hickey family (pictured above) geocached, or a graveyard. I can tell you about a quiet one in the north of Maine.