Return now to a new warning for air travelers this morning. The department of homeland security issued an alert about a possible shoe bomb attack. ABC's Pierre Thomas following the story for us this... See More
Return now to a new warning for air travelers this morning. The department of homeland security issued an alert about a possible shoe bomb attack. ABC's Pierre Thomas following the story for us this morning. Good morning, to you, Pierre. Reporter: Good morning, josh. Today U.S. Authorities are warning the airlines that terrorists are refocused on finding ways to blow commercial planes out of the sky. Sources tell ABC news new credible intelligence obtained from overseas suggests that terrorist bombmakers have stepped up efforts to build shoe bombs to design liquid explosives and to hide them in cosmetic containers, the goal, to smuggle bombs on commercial international flights. No specific plot has been identified but the threat is being taken seriously. Passengers flying to the U.S. From overseas can expect to see additional pat-downs and extra scrutiny of their shoes and carry-on items. I think aviation symbolizes something to Al Qaeda, the idea that you can take down a plane and kill potentially hundreds of people, both that are on the plane and on the ground is very appealing. Reporter: In some ways this is security deja Vu. In December 2001 only three months after 9/11, Richard Reid boarded a u.s.-bound plane with 197 passengers with plastic explosives built into the heel of his shoe. The bomb failed to detonate when he tried to set it afire. But this simulation shows what it could have done. The attempts to take down planes continued. There was the london-based liquid explosives plot to blow up planes over the atlantic and the underwear bomber trying to take down a plane on Christmas day over Detroit. With thousands of Americans about to head home from the sochi olympics you can see why authorities are taking no chances.
This transcript has been automatically generated and may not be 100% accurate.