Starfish Prime

The US caused the death of he world's first commercial satellite (TELSTAR) only a few months after it was launched. We set of a nuclear blast in space (5, actually) and that blast (Starfish Prime) created an electro-magnetic pulse (EMP) that killed TELSTAR (which was placed in orbit the day AFTER the test; the EMP effects energized the Earth's magnetic field lon enough to cause the satellite to die on orbit). The govt didn't tell AT&T what happened until around 2005 or so. (Whoops, our bad.......sorry)

Starfish Prime Wikipedia entry