The AAA estimates that more than 100 million Americans will travel at least 50 miles over Christmas and New Year's for the first time.

Most holiday travelers will be driving this year, but heightened airport security measures may cause inconvenience for the nearly 6 million who are expected to get on an airplane. In light of the Paris attacks, the TSA is changing its passenger screening protocols regarding airport body scanners, reports CBS News correspondent Jeff Pegues.

The Department of Homeland Security quietly made these changes last week.

DHS officials wrote in a document that the TSA was updating "the ability of individuals to opt-out of AIR (Advanced Imaging Technology) screening in favor of physical screening." This now clears the way for the TSA to "direct mandatory body scanner screening for some passengers as warranted by security considerations."

Over the years, the technology has evolved. Those body scanners that some critics labeled "virtual strip searches" are gone in favor of machines which replace an individual's image with that of a generic figure. Officials believe this lessens privacy concerns.

Airport security has been under the microscope. Over the summer, a scathing DHS Inspector General report uncovered major gaps. Investigators discovered that 95 percent of the time, they were able to smuggle mock explosives or banned weapons through checkpoints - in some cases, cruising through TSA pat-downs.

It led to a security overhaul that DHS Secretary Jeh Johnson talked about again just last week.

"In July, I gave the new administrator at TSA a 10-point plan for improving aviation security and airport screening domestically," Johnson said. "That plan has been and is being implemented on schedule."

The body scanning machines are extremely sensitive. Experts say they can pick up something like a handkerchief tucked in the pocket. But most importantly, they can detect non-metallic explosives, which is what officials say terrorists are trying to smuggle on planes.