Jan. 6, 2010 -- Just when airline passengers were getting used to life in the post-9/11 world, Abdul Farouk Umar Abdulmutallab threw airport security on its head. He is the one who allegedly tried to blow up a Northwest Airlines plane on Christmas day.
Now travelers looking to fly are faced, yet again, with a new set of rules and procedures and are once again struggling to figure out how life at the airport has changed.
The Transportation Security Administration has not publically spelled out all the security details (why share that information with the terrorists, right?) but has instead described its new procedures as a "layered approach."
But what does that mean? ABC News has tried to sort through it all and give you this guide on how air travel is different for you today.
Will You Notice Anything Different At Airports?
Not necessarily. There have been reports of some longer lines at security. And everybody is a bit more on edge these days because of the attempted Christmas attack, which can also mean it takes longer to clear the checkpoint. The TSA said that some of its measures are clearly seen by people while others might be hard to detect.
What Additional Steps Are Being Taken?
The TSA said it has the ability to "quickly implement additional screening measures," including explosive detection canine teams, extra law enforcement officers, additional screening at the gates, behavior detection and other unspecified measures.
Why Do Some Airports Handle Security Differently?
The basics of airport screening -- you know, take off your shoes, remove your laptop and jacket and walk through the metal detector -- remain the same. But the TSA warns that passengers should not expect to see the same thing at every airport. That warning generally refers to the extra measures such as additional gate checks or canine teams. What About International Flights?
Immediately following the Christmas Day attack, the government required all passengers on international flights to stay seated for the final hour of the journey and have nothing on their laps. The government has since relaxed that rule, leaving it up to individual flight crews, for now, to determine what rules to impose on passengers.
Do International Travelers Face Additional Requirements?
Yes, this week the TSA started requiring all passengers on flights from certain countries to go through an "enhanced screening" process. Some international passengers told ABC News that they underwent thorough bag searches and were patted down.
The TSA is only requiring such searches for people who are "traveling from or through nations that are state sponsors of terrorism or other countries of interest." A senior government official told ABC News that those countries are: Afghanistan, Algeria, Iraq, Lebanon, Libya, Nigeria, Pakistan, Saudi Arabia, Somalia, or Yemen, or one of the following countries designated as state sponsors of terrorism: Cuba, Iran, Sudan, and Syria.
Have the Allowed Carry-On Items Changed?
No. The TSA says that for passengers departing U.S. airports the security checkpoint requirements remain the same.
Should Passengers Arrive at the Airport Earlier Than Normal?
The TSA suggests extra time for international flights heading to the United States but otherwise avoids specifics, advising passengers to check with the airport or their airline. The TSA used to list average airport checkpoint wait times on its Web site but a new calculator has been "under construction" for several weeks, since before the attempted Christmas attack.
So How Long Will These Measures Remain?
Nobody is sure. Some people are calling for a complete overhaul of the nation's aviation security procedures. Others say that once this incident is out of our immediate memories, security will be relaxed to speed up the travel process. All the TSA will say for now is that it "will continuously review these measures to ensure the highest levels of security."
What About Those Terrorist Watch Lists and No-Fly Lists?
U.S. officials tell ABC News that since the attempted plane bombing on Christmas Day, the government has intensified efforts to check whether individuals on terror watch-lists hold valid U.S. visas. One senior US official tells ABC that so far the effort has resulted in the revocation of at least five visas.
Airport Security: What Has (and Hasn't) Changed
Comparing terror lists to visa records has been standard practice since 9/11, resulting in more than 1,700 visa revocations since then, but the sources say this effort has picked up since the underwear bomber was able to board a US.. bound flight despite being put on the a mild watch list because nobody bothered to do a simple search for his visa records.
One source tells ABC News that the Obama administration is looking to expand the no-fly lists in the wake of last month's attempt, adding dozens of names that had been on lower-priority watch lists.
"There's already been a rescrubbing of all the different lists," White House deputy spokesman Bill Burton told reporters.
There are approximately 550,000 names in the Terrorist Identities Datamart Environment (TIDE) list and roughly 400,000 names in the Terrorist Screening Data Base (TSDB).
"Based on age and nationality criteria" extrapolated from the recent plot, the government has identified dozens of people from those two lists and added them to a more-stringent "Selectee List."
The Selectee List has approximately 16,000 individuals who require more stringent screening before they are permitted to board an airplane. The No-Fly list has about 4,000 other individuals.
With reports from Pierre Thomas, Kirit Radia and Jake Tapper