Thousands of green cards have been mishandled over the past three years, according to a new Department of Homeland Security inspector general report. Electronic system errors have caused at least 19,000 cards to be issued as duplicates or with incorrect information - such as name, date of birth, photo and gender - the report says.But the head of U.S. Customs and Immigration Services (USCIS), which manages immigration benefits, said that several of the report's conclusions were overstated.The USCIS director said that the agency did not issue green cards to any individuals who were not eligible to receive them and that the number of cards containing errors were only a "tiny percentage" of the total issued each year.He added that for the cards to be misused, they would have to fall into the hands of someone with "malicious intent" and a physical resemblance to the card's intended recipient.In some cases, green card applicants who should have received a card good for two years were issued one valid for 10 years.During the past year, USCIS inadvertently sent more than 6,000 duplicate green cards to applicants."It appears that thousands of green cards have simply gone missing. In the wrong hands, green cards may enable terrorists , criminals and undocumented aliens to remain in the United States," said DHS Inspector General John Roth.The report follows up on the watchdog's March finding that USCIS possibly sent hundreds of green cards to the wrong addresses.The problem was "far worse than originally thought," according to Roth.In September, Roth found that because of issues with USCIS digital fingerprint records, the U.S. government mistakenly granted citizenship to at least 858 immigrants who had pending deportation orders.New information on the scope and volume of issues prompted the publication of today's report.The majority of the card issuance errors were due to "flawed design and functionality problems" with the agency's electronic immigration system, which was implemented in 2013, according to the report.It also found that the percentage of green cards issued in error has steadily increased each year since the system was put into use.The watchdog said that USCIS "lacked consistency and a sense of urgency" in its efforts to recover the inappropriately issued cards, despite previous findings."We must take concrete steps to remove any security gaps that can be exploited by terrorists and criminals. U.S. Citizenship and Immigration Services can assist such efforts by strengthening quality controls and its procedures to target lost, stolen or erroneously issued green cards," said Senate Homeland Security Committee Chairman Ron Johnson, R-Wis., in response to the report.Over the last three years, USCIS received more than 200,000 reports from approved applicants about missing cards, said the report.The mistakes were costly. The agency spent just under $1.5 million to address card-related issues in fiscal year 2015, said the report.The immigration agency agreed with all the report's recommendations - including fixing the electronic system and implementing internal controls to identify issues early in the process - and said the measures will be implemented by June 2017.