Cybersecurity teams are working feverishly to stem the impact of the single biggest global ransomware attack on record.

Businesses around the world rushed Saturday to contain a ransomware attack that has paralyzed their computer networks, a situation complicated in the U.S. by offices lightly staffed at the start of the Fourth of July holiday weekend.

A ransomware attack has paralyzed the networks of at least 200 U.S. companies.