This is not the pudding Bill Cosby made famous.
The exact stores where the pudding was discovered have not been identified but police confirmed that one was in Woodbury.
Four tainted packages have been discovered over the past two days.
In each case, police said, the pudding mix was emptied from the boxes and then replaced with another substance. Early tests indicated that it may have been aquarium sand, police said.
The repackaged boxes were later returned to the stores -- and cops say they may have been exchanged for a refund and then restocked on the shelves.
Preliminary lab tests indicate the substance poses no danger to the public, say police.
Investigators have warned the public to exercise caution with any food package which appears to have been opened.