More than half a million aliens overstayed their temporary visas in the United States in 2015, with more than 482,000 of those individuals believed to be still residing illegally in the United States, according to a new report by the Department of Homeland Security.

Around 527,127 aliens temporally granted U.S. business and tourist visas were found to have stayed in the United States longer than legally permitted, according to DHS’s 2015 entry and exit overstay report.

Of those who did not leave the United States on time, around 482,781 are believed to still be illegally residing in the United States, according to the report, which was issued by DHS amid debate in Congress over an Obama administration initiative to permit around 170,000 new immigrants from Muslim-majority nations in 2016.

Senior Obama administration officials had trouble in the past year informing Congress about the number of individuals who had overstayed their visas. The administration also could not provide Congress with statistics about the number of Syrian refugees who had been granted residency in the United States in 2015.

Concerns about visa overstays come as Congress is investigating a sharp uptick in the number of terror plots hatched by foreign-born individuals legally granted entrance to the United States. Lawmakers estimate that at least 113 foreign-born individuals have been implicated in domestic terror plots since 2014.

Last year there were 219 illegal overstays from Afghanistan, 681 from Iraq, 564 from Iran, 56 from Libya, 1,435 from Pakistan, 440 from Syria, and 219 from Yemen, according to the report. Many are still in the United States illegally.

Click for more from The Washington Free Beacon.