Homeland Security Secretary, Michael Chertoff announced today that visitors who can travel to the United States will be required to register biographical details online at least three days before their visit.

The changes will affect travelers from countries whose citizens are not required to obtain visas for U.S. entry.

Chertoff says the program will allow the U.S. to screen visitors before they travel. The program will take effect in August, and will be mandatory for all visa-free travel by January 12.

Twenty-seven countries are currently in the U.S. visa-waiver program. More are expected to join later this year.