Today, the Government Accountability Office issued a report of preliminary finding on the progress the Department of Homeland Security has made in its efforts to reduce the backlog of immigrant visas. Although almost 863,000 records were "closed" in the last two years, the backlog of potential overstays remains at more than one million [emphasis added]:
In the summer of 2011, DHS reviewed the 1.6 million potential overstay records. As a result, DHS closed about 863,000 records and removed them from the backlog. Since that time, DHS has continued to review all potential overstay records for national security and public safety concerns. However, as of April 2013, DHS continues to maintain more than 1 million unmatched arrival records in ADIS. GAO's preliminary analysis identified nonimmigrants traveling to the United States on a tourist visa constitute 44 percent of unmatched arrival records, while tourists admitted under a visa waiver constitute 43 percent. The remaining records include various types of other nonimmigrants, such as those traveling on temporary worker visas.
The report does note a change implemented since the Boston bombing related specifically to student visas:
Beginning in April 2013, ICE’s Student and Exchange Visitor Information System (SEVIS) began automatically sending data to ADIS on a daily basis, allowing ADIS to review SEVIS records against departure records and determine whether student visa holders who have ended their course of study departed in accordance with the terms of their stay. Prior to this date, DHS manually transferred data from SEVIS to ADIS on a weekly basis. According to DHS officials, these exchanges were unreliable because they did not consistently include all SEVIS data—particularly data on “no show” students who failed to begin their approved course of study within 30 days of being admitted into the United States.
DHS has yet to comply with federal law requiring reporting of visa overstays, but the GAO notes that Janet Napolitano has said that DHS intends to begin such reporting by the end of the year:
Federal law requires DHS to report overstay estimates, but DHS or its predecessors have not regularly done so since 1994. In September 2008, GAO reported on limitations in overstay data that affect the reliability of overstay rates. In April 2011, GAO reported that DHS officials said that they have not reported overstay rates because DHS has not had sufficient confidence in the quality of its overstay data and that, as a result, DHS could not reliably report overstay rates. In February 2013, the Secretary of Homeland Security testified that DHS plans to report overstay rates by December 2013.