Alan Gomez

USA TODAY

More than 600,000 foreign travelers who legally entered the United States in 2016 overstayed their visas and remained in the country at the end of the year, the Department of Homeland Security reported Monday.

Those "visa overstays" represented only 1.25% of the 50 million travelers who arrived in 2016 through the nation's airports and seaports. People who overstay their visas make up an estimated 40% of the 11 million undocumented immigrants who live in the U.S. They are largely overshadowed by undocumented immigrants who cross the southwest border with Mexico.

The department changed the way it calculates visa overstays, but an analysis of the most popular visa categories shows a 13% increase in overstays in 2016 from the previous year.

Little has been known about the population in the past. Homeland Security issued the first report on visa overstays in January 2016. Monday's report gives government officials and immigration researchers a second year of data, possibly providing insights into countries or visa categories that may warrant closer scrutiny from immigration officials.

The Trump administration will also use the data to seek and capture people who overstayed their visas. Homeland Security said that it provides daily, updated information of people who overstayed their visas to Immigration and Customs Enforcement (ICE), the agency responsible for enforcing immigration laws in the interior of the country.

"Identifying overstays is important for national security, public safety, immigration enforcement, and processing applications for immigration benefits," the report said.

According to the report, a total of 739,470 foreigners remained in the U.S. in 2016 for some period after their visas had expired. But not all of those are here to stay. By Sept. 30, 2016, which represents the end of the 2016 fiscal year, the number fell to 628,799. By January, the number was down to 544,000.

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Nearly 500K foreigners overstayed visas in 2015

Biometric tracking a hurdle for immigration bill

Homeland Security changed the visa categories that it used to make the report for 2016, meaning the total number of visa overstays cannot be compared with the previous year.

In 2015, 347,632 foreigners who entered the U.S. through the Visa Waiver Program, B-1 business visas or B-2 tourism visas, ended up staying in the U.S. after their visa had expired. That number rose to 392,276 in 2016, representing a 13% increase.

The administration will also continue a decades-long effort to implement a more sophisticated "exit-entry" system that allows the federal government to better track people who are here on short-term visas.

The U.S. currently uses "biographic" information to track people, relying on airline manifests that list each passengers name, date of birth and other basic information. Several Democratic and Republican administrations have tried to improve that system to use "biometric" information, such as fingerprints and iris scans. Homeland Security continues to run studies and pilot projects to figure out how to implement that kind of program, but has been unable to make much progress.