As stores staff up for the winter holidays, they should know that they are likely bringing on more than a few thieves in the process. A new report from loss prevention firm Checkpoint Systems finds that the biggest share of theft at retailers comes from employees, not shoppers, as Marketwatch reports.

The report shows that employee theft accounts for nearly 43 percent of US retail "shrinkage" — an industry term for the difference between recorded and actual inventory. That amounts to $18 billion — roughly $2.3 billion more than stores lose to shoplifting, Marketwatch reports.

Other reports have shown similar patterns. In 2012, the National Retail Federation likewise found that employee theft outstripped shoplifting, roughly 44 to 36 percent.

Interestingly, US workers appear to be far more dishonest than those overseas. The report also finds that while 43 percent of shrinkage in the US is due to employees, it's only 28 percent overseas, where shoplifters are instead the bigger problem, accounting for 39 percent of shrinkage.

On the other hand, US firms have been known to steal from their employees in the form of wage theft, like unpaid wages. Attorneys, state, and federal agencies recovered more than $900 million in lost wages in 2012, according to one report from the left-leaning Economic Policy Institute, which has also estimated that wage theft could be costing US workers $50 billion a year.