Thirteen percent of the H-1B visas granted are based on fraud and another 8% contain so-called technical violations, according to a study just done by the U.S. Citizenship & Immigration Services (USCIS), an arm of the Department of Homeland Security, and forwarded to the Senate Judiciary Committee.

The USCIS processes visa petitions and, given the findings, says it's making procedural changes that haven't been disclosed yet.

The study, which found that 27% of the sample computer-related visas were tainted, documents cases of bogus credentials and degrees and people not working where they were supposed to be working or doing what they were supposed to be doing, not getting prevailing wages, and using the visa to re-enter the U.S. after they were fired or quit

See http://grassley.senate.gov/private/upload/100820081-3.pdf for the study.