KAREN ROWAN: Could Extraterrestrials Really Invade Earth, and How? I don’t find this story particularly thoughtful. Aliens wouldn’t have to send an army. A quarter-pound of lethal nanobots would do for a planet — and paranoid aliens would send them just out of fear that a hostile intelligence might evolve some day.

A good fictional treatment is in Greg Bear’s The Forge Of God, For the more technically-inclined, there’s Ernst Fasan’s Relations With Extraterrestrial Intelligences, or some chapters in McDougal, Lasswell, and Vlasic’s Law and Public Order In Space. Kind of old, but still good. A more recent popular treatment that’s worth your time is Ben Bova and Byron Preiss’s Are We Alone in the Cosmos? The Search for Alien Contact in the New Millenium.