From the NJ.com:
Those who received warnings were told the state had no way of knowing whether their information was sent incorrectly.
“This letter is to inform you that due to an error at the Department of Labor and Workforce Development your name and Social Security number may have been accidentally delivered to an employer for which you did not work,” the letter reads.
The mistake came because, due to the staggering amount of layoffs in New Jersey, quarterly reports listing former employees who were receiving unemployment benefits were, in some cases, too long and had to be stuffed by hand.
Some lists got stuffed into the wrong envelopes. The error was discovered when seven companies reported receiving the wrong list of names.