BUTTE, Mont. -

Butte-Silver Bow police say local businesses need to be on alert for counterfeit cash.

A fake $50 dollar bill turned up at the Butte Walmart. Other counterfeit bills have been found at at least three other businesses.

Authorities said by the looks of it, they could be linked to series of fake $20 and $50 bills found circulating in Butte, Dillon and Deer Lodge.

Police said businesses should use a special pen to test all bills $20 and up.