More than 800 immigrants from countries posing a national security threat are legally calling the United States home at the government’s expense after they were mistakenly granted citizenship. According to an internal audit released Monday by the Department of Homeland Security, all 858 of the immigrants that had been granted citizenship were pending deportation orders, the Associated Press reported.

The report stated that the immigrants used different names and fabricated birthdates to apply for citizenship. U.S. Citizenship and Immigration Services were unable to catch the immigrants because their fingerprints were not accessible on the government database. It was not immediately clear when the immigrants were granted citizenship, and the digital fingerprint system wasn't instituted until 2010.

None of the immigrants’ names nor their home countries were released. However, Inspector General John Roth’s audit did confirm the immigrants were either from “special interest countries” or nearby areas known for high immigration fraud rates. The report also noted that nearly 315,000 fingerprints of immigrants with final deportation orders and fugitive criminal records are missing from the database, and Immigration and Customs Enforcement still has about 148,000 respective immigrants’ files to review in order to add fingerprints to the digital record.

Awarding citizenship to deportees can pose a serious threat to national security. Immigrants given full citizenship are able to apply for and obtain security clearances, as well as accept security-sensitive jobs in the US. Roth’s report cited at least three immigrants who were cleared for citizenship that managed to obtain aviation or transportation worker credentials, which allows them employment-based access to security-regulated areas of airports, maritime buildings and sea craft. However, these specific immigrants’ security clearances have since been revoked after the revelation.

The news comes as Republican presidential nominee Donald Trump advocates for a stricter immigration policy should he take the White House in the upcoming November 8th election. While speaking in Arizona earlier this month, Trump preached a “no amnesty” campaign for undocumented immigrants in the US. Along with building a “beautiful” and “impenetrable” wall along the Mexican border, he also promised voters he’d stop illegal immigration. Under his immigration reform, Trump promises to return all undocumented immigrants to their homelands, beef up the consequences for those staying in the U.S. after their visas expire and put a complete end birthright citizenship — the automatic granting of citizenship to children born in the U.S. regardless of their parent's immigration statuses.

President Barack Obama's administration reported deportations for approximately 414,481 undocumented immigrants in the US in 2014 — which was considered a big drop in deportation rates. However Obama's presidency is responsible for the highest number of deportations of any other president. There were still 2.5 million cases of deportations reported from fiscal 2006 to 2014.