A cyberattack on JBS SA, the world’s largest meat producer, has forced the shutdown of some slaughterhouses globally, and there are signs that closures are spreading. JBS’s five biggest U.S. beef plants, which combined handle 22,500 cattle a day, have halted meat processing, according to company Facebook posts, employees and labor unions, following the Sunday attack on the company’s computer networks. Slaughter operations in Australia had already been halted, according to a trade group, and one of Canada’s largest beef plants was idled for its second day on Tuesday. The prospect of more extensive shutdowns around the world is already upending agricultural markets and raising concerns about food security as hackers increasingly target critical infrastructure. In the U.S. alone, JBS accounts for almost a quarter of all beef capacity and nearly a fifth of all pork capacity. Livestock futures slumped.