The Department of Homeland Security (DHS) reported Monday that more than 600,000 foreign travelers legally entered the U.S. in 2016 and then overstayed their visas.

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

The report described “an overstay [as] a nonimmigrant who was lawfully admitted to the United States for an authorized period, but remained in the United States beyond his or her period of lawful admission.”

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The document said 739,470 foreigners remained in the U.S. in 2016 for some time after their visas expired.

The number dropped to 628,799 foreigners by Sept. 30, 2016, it said, the end of fiscal 2016, before reaching 544,000 foreigners in January.

USA Today on Monday reported that the DHS had changed the visa categories it used to make the report for 2016, meaning the total number of visa overstays cannot be compared with the previous year.

The newspaper reported that 347,632 foreigners entered the U.S. in 2015 through the Visa Waiver Program, B-1 business visas or B-2 tourism visas before overstaying once their visas expired.

USA Today reported that number rose to 392,276 last year, marking a 13 percent increase in visa overstays.

People overstaying their visas make up an estimated 40 percent of the 11 million undocumented immigrants living in the U.S., it reported.

Visa overstays reportedly represented about 1.2 percent of the 50 million people who arrived in the U.S. in 2016 through America’s airports and seaports.