Clear evidence that US employers knowingly hire illegal workers

I discovered at Econbrowser the following statement from a story in the Arizona Republic...

"A 2005 report by the federal Government Accountability Office found that between 1985 and 2000, 9 million people got hired using this Social Security number: 000-00-0000. The report also found 3.5 million instances where a company had several employees using the same Social Security number. Most of the problem entries came from the food service industry and the construction industry."