U.S. Citizenship and Immigration Services got good news and bad news in a recent independent evaluation of its controversial E-Verify program, used to determine whether workers are authorized to work in the U.S.

The good news: Just more than 93 percent of all E-Verify cases involved legal workers who were correctly identified as employment authorized, while only 0.7 percent involved legal workers wrongly identified as unauthorized.

The bad news: The remaining 6.2 percent were unauthorized workers, but the system failed to flag more than half of those. The report attributed the missed illegal workers to the system's inability to detect some instances of identity fraud.

Immigration reform advocates have frequently criticized E-Verify for database inaccuracies that jeopardize the job opportunities of legal immigrants, but the report showed that the system more frequently allows illegal workers to obtain positions.

All federal contractors are required to use E-Verify, and several states have mandated use of the system, which matches identity information provided by the worker against Homeland Security and Social Security databases.