In the biggest change since the attacks of September 11, 2001 drastically increased airport security around the US, the Department of Homeland Security has just announced that airline passengers can now keep their shoes on while passing through TSA checkpoints.

The change, which was issued by memo to TSA agents last week and reported on by CBS News Monday, allows all airline passengers in the regular TSA lines at airports — not just Pre-Check — to keep shoes on when going through checkpoints. The policy shift will roll out in phases, but it's already taken effect at San Francisco International Airport as of Tuesday, per the Chronicle.

Other airports on the first-phase list include Baltimore/Washington International Airport, Fort Lauderdale International Airport, Cincinnati/Northern Kentucky International Airport, Portland International Airport, Philadelphia International Airport, and Piedmont Triad International Airport in North Carolina. And CBS News reported the shoe rule had lifted at LAX and New York's LaGuardia Airport as well. The goal is to have the policy change at all airports soon.

White House Press Secretary Karoline Leavitt retweeted the CBS News report on Tuesday morning, but offered no further explanation.

According to Homeland Security, footwear can remain on unless it sets off alarms at scanners or magnetometers, in which case it will need to be removed for further scanning. A statement from HSA said, "We are always exploring new and innovative ways to enhance the passenger experience and our strong security posture."

As some of us may remember, the practice of taking off shoes at airports began in 2006, a full five years after the thwarted terrorist incident that inspired it. And that incident didn't even involve a passenger going through security in the US.

Three months after the 9/11 attacks, on December 22, 2001, London-born petty criminal Richard Reid, who had become radicalized and received terrorist training in Pakistan, boarded American Airlines Flight 63 from Paris to Miami. In the middle of the flight, Reid began trying to light the fuse on one of his shoes, which was packed with explosives, in an attempted suicide bombing — but the fuse failed to light. Passengers subdued him, the plane made an emergency landing in Boston, and Reid was arrested. He remains in federal prison serving a life sentence.

It's not clear what technology now exists to detect a similar "shoe bomb," except maybe the full-body scanners, which most major airports now use.

It's been the practice at SFO and elsewhere, at least on busier travel days in the last two years, to streamline the security process by using bomb-sniffing dogs in the TSA lines — you may have done the two-by-two walks past them — and then allowing travelers to keep electronics and liquids in their bags before sending them through the scanners. Occasionally this was combined with a lifting of the shoe-removal policy.

And even though Reid had been on an international flight into the US, the shoe-removal practice was very much an America-only thing. Flights out of Europe, Asia, and Canada generally have never required this, except for a brief period two decades ago when Europe followed suit with the US.

Top image: Travelers go through the TSA PreCheck security point at Miami International Airport on June 2, 2016 in Miami, Florida. As the busy summer travel season heats up the Transportation Security Administration is encouraging people to sign up for the TSA PreCheck program to save time going through the airports security lines. Those enrolled in the program can leave their shoes, light outerwear and belt on during the terminal screening process as well as keeping their laptop in the carry-on suitcase without having to remove them at the checkpoint. (Photo by Joe Raedle/Getty Images)