I heard it on the radio yesterday while reloading ammo.  It's on the web now:

Idaho 55 at the Rainbow Bridge was closed for about six hours Tuesday after a suspicious object was found underneath the bridge.

An ITD spokesman said investigators were conducting a routine bridge safety inspection around 9:30 a.m. today when they saw an object they could not identify. It was a green bucket with wires poking out.

Idaho State Police and the Boise Bomb Squad were called in to investigate and 17 miles of highway was closed. Investigators determined the bucket was filled with trinkets, photos and toys placed there as part of an online scavenger hunt called geocache. Players use a global positioning system to find the treasure.

Police say the man who stashed the object under the bridge has come forward and charges might be filed against him.

As it was said in a geocaching forum:

Consider. If all it takes to shut down the country is to toss ducted tape tupperware full of rocks with an old radio in it out the side of your window while you are driving down the interstate, then it won't be long before terrorists start causing disruption in a mass scale by doing exactly that. 

There are an almost infinite number of things we can't and shouldn't defend against.  Money is better spend attacking the root of the problem--extremist Muslims.  We must destroy their culture.