According to Ross, government sources have also indicated that U.S. intelligence officials received intelligence reports two weeks ago warning of terror attacks in Glasgow and Prague against "airport infrastructure and aircraft."
Chertoff denied that today on "Good Morning America," saying, "We didn't have any specific, credible information about an imminent attack in Glasgow."
One former CIA and State Department counterterrorism official believes the United States is justified in keeping the terrorist alert at its current level. He believes officials are overreacting by increasing security at the airports.
Larry Johnson, who now works as a terrorism consultant, said, "doing this is more about politics than security ... there is no reason to do this."
Johnson said, "It would be one thing if they had intelligence showing people are planning on loading a car with an IED [mprovised explosive device] and driving into an airport. We don't have that kind of intelligence."
"The reality," Johnson said, "is that these kinds of incidents are very infrequent and very rare ... and good law enforcement and intelligence can go a long ways toward thwarting these things."
Brian Jenkins, an analyst at the Rand Corp., believes the government is correct to increase security. "It's just a matter of prudence," he said. "Let's lean forward a little in the foxhole and take it up a notch."
Jenkins said events like those in Great Britain often inspire copycats and hoaxes. "Whether it's a genuine jihadist or a malicious crankster, they could think this is the time to act," he said.
He also believes the increased security may help reassure the public, and that if the Department of Homeland Security failed to increase security and an "event occurs, then people will say, 'Why didn't you do something?'"
Jenkins agrees with Johnson that there is always a political calculation to decisions to increase — or decrease — security.
Johnson believes that adding patrols and searching cars have a measurable effect on security, but he insisted, "we need to be far less reactive, or react when we know there is something we can do to truly change the threat picture and make people safer, as opposed to inconveniencing people over a holiday weekend."