I’ve travelled quite a bit in the past, but I didn’t even know about this: US Customs and Border Protection agents can "randomly" seize your laptop, camera, cell phone and other electronic devices at the border for inspection - meaning they’ll take a peek at what you’ve got stored in your machine:
Bill Hogan was returning home to the U.S. from Germany in February when a customs agent at Dulles International Airport pulled him aside. He could reenter the country, she told him. But his laptop couldn’t.
U.S. Customs and Border Protection agents said he had been chosen for "random inspection of electronic media," and kept his computer for about two weeks, recalled Hogan, 55, a freelance journalist from Falls Church, Va.

But don’t they need a warrant to do that? Nope - no, they don’t:
Authorities need a search warrant to get at a computer in a person’s home and reasonable suspicion of […]

Original post by Alex