BOSTON -- An ex-dairy farm worker is facing up to three years in prison for a prank that left a razor blade in a carton of Edy’s Cookies ’N Cream ice cream.

Stephen O’Brien pleaded guilty Tuesday to one federal count of tampering with a consumer product, the Boston Herald reported. He could get up to three years in jail and a $350,000 fine when he's sentenced in September.

Authorities said O'Brien and two co-workers at Whitman’s Dari-Farms Co. were "screwing around" in February 2007 by stabbing ice cream cartons with razors used to cut shrink wrap.

He said one of the razors broke off and he meant to throw the carton out, but it ended up at a Hooksett, N.H., Target store where workers at an in-store snack bar discovered it and threw it out. No one was hurt.

Dari-Farms said it recalled all the packages that O’Brien and his pals might have handled, according to Whitman police.

O'Brien was fired, as was a co-worker who allegedly spat into one of the cartons.