NEW YORK (CBSNewYork) — As millions fly home for the holidays, CBS News has learned that a controversial part of the screening process at the nation’s airports was quietly changed last week.

The change concerns body scanners.

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The Department of Homeland Security wrote in a document obtained by CBS News that the Transportation Security Administration was updating “the ability of individuals to opt-out of AIT (Advanced Imaging Technology) screening in favor of physical screening.”

While passengers can typically opt out of an AIT screening for a physical screening, the new rule will make it mandatory for some passengers to go through the body scanners.

“Some passengers will be required to undergo AIT screenings as warranted by security considerations in order to safeguard transportation security,” a TSA spokesperson said in a statement.

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The DHS said the scanners are used to screen passengers for prohibited items including weapons, explosives and other “threat objects” that could be hidden under clothing.

Full body scanners were introduced at airports to a flurry of controversy. Opponents said the detailed image of the human body provided by the machine is an invasion of privacy, while others argued the level of radiation emitted by the Backscatter scanners could be dangerous over the long term.

The machines now offer a generic image of the human body and highlight the location of objects on a person. The DHS said the machines do not have the ability to store images.

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If an object is detected, TSA agents would pat the area and possibly perform a more comprehensive search, the DHS said.