Former CIA official: New shoe bomb alert suggests screening flaw found

The federal government is asking airlines to watch out again for shoe bombers. Homeland Security officials say there's no specific threat, but an intelligence source told CBS News the alert is based on recent terrorist chatter.

The new warning applies to flights to the United States from other countries. It focuses on explosives that can be hidden in shoes, liquids or cosmetics.

CBS News senior security contributor Mike Morell, a former deputy CIA director, said he's more worried about this threat than some of the others in recent weeks. He said, "The fact that it's only chatter does not give me any comfort."

He continued, "Some of the most significant attacks that we've seen over the last 10 years have been preceded by chatter - most importantly 9/11. The fact that the terrorists are coming back to shoes is also worrisome to me because it suggests that they may have found a way around the screening that is currently done on shoes."

Though it's unknown where the threat is coming from, Morell said his guess would be from al Qaeda in Pakistan or in Yemen. "Those are the two places in the world that continue to want to attack the U.S. homeland, so that's why I'm focusing on those," he said. "Most likely, in my mind, Yemen."

Ibrahim al-Asiri - al Qaeda's No. 1 bomb maker, who is in Yemen - is the biggest concern, according to Morell, who described al-Asiri as "very, very creative" and who may be behind the latest threat.

"He's the guy that brought you the underwear bomb," said Morell. "He's the guy that brought us the non-metallic suicide vest, and if he has found a way to be creative with shoe bombs, then that is something we need to worry about."

Morell added, "I'm concerned that he may have found a way to put explosives in shoes that get around the current screening procedures."

Travelers, Morell said, are likely to see a greater percentage of shoes being tested for explosives after they go through the metal detector.