WOODBRIDGE - Businesses in Middlesex County are being warned about a rash of counterfeit $100 bills being passed around.

Investigators say that whoever is making the fake $100 is doing it by doctoring real $5 bills to look like $100.

Two of the fake bills were used at the M-Gyro shop in Fords. The restaurant’s security system caught the two suspects in the act. One allegedly paid for a small food order with the phony $100. The other suspect was allegedly given change for another fake $100.

When the M-Gyro employee tested the bills using the currency marker, the marking showed the bills were legit, since a real $5 bill was actually used.

As many as six Woodbridge restaurants and stores, mostly in the Fords or Colonia neighborhoods, have been fooled by bogus bills.

Police caution businesses to be extra careful, and know about other ways to test the authenticity of currency. Most paper bills will have a hologram inside. The hologram will match the face on the bill.

Anyone who might have any information about these crimes should contact the Woodbridge Police Department.