The federal government is tightening security at airports, seaports, border crossings and federal buildings in response to the Feb. 7 elevation of the national alert level to orange, or "high risk" of terrorist attack.

But what can the private sector, which controls 85 percent of the nation's infrastructure, do?

"The No. 1 thing to be aware of, is unusual interest in your facility," said Ross Bulla, president of The Treadstone Group, a Denver, N.C., security and investigative company.

Organized terrorist attacks are usually preceded by lengthy surveillance day and night, Bulla said, so "look for unusual interest in your facility, people taking photographs or videotapes, asking unusual questions."