Prices for some processed American cheeses are plummeting as the largest U.S. manufacturer quietly recovers from a cyberattack.

Schreiber Foods in Wisconsin was forced to shut down operations after a cyber event on Oct. 23, a spokesperson said. The attack targeted systems that keep plants and distribution centers running.

The company buys cheese in 500-pound barrels and then turns it into slices that go on a burger or into a sandwich. When it stopped purchasing because of the attack, the barrels piled up, Matt Gould, editor of The Dairy Market Analyst, said in a note. Schreiber’s operations were back online by Oct. 28.

Spot prices for cheese barrels traded in Chicago plunged 17% last week, the most in about a year.

The world’s food supply chains are being tested by logistics and shipping chaos at a time when global demand is on the rise. Cyberattacks are adding to the uncertainty, with meat giant JBS SA and an Iowa grain cooperative also targeted this year.

Other bearish signs for cheese include port conditions on the U.S. West Coast getting significantly worse this week, which is likely resulting in cancellations of cheese shipments, Gould said.