Nightline have just changed their planned broadcast for tonight. They're shelving a piece on North Korea for an interview with Tom Ridge on why the domestic security alert level was raised to "orange" today.

Here's the Nightline advisory:

Nightline's focus for tonight's broadcast has changed, due to breaking news.

The White House raised the national terror alert this afternoon from yellow to orange, the second-highest level in the color-coded system. Attorney General John Ashcroft cited an "increased likelihood" that al-Qaeda would attack Americans, either at home or abroad. The change in the terror alert status has already triggered some increased security precautions at the federal and local levels.

The Attorney General warned that apartment buildings, hotels or other "lightly secured targets" in the United States could be vulnerable. He added that terrorists might seek "economic targets, including the transportation and energy sectors, as well as symbolic targets and symbols of American power."

A broad description, to say the least. So, how should you or I change how we conduct our lives? And what is different about the conversations U.S. intelligence officials are eavesdropping on these days? What triggered this?

Ted Koppel will talk with the Secretary of the newly created Department of Homeland Security, Tom Ridge, tonight.