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.

It’s not yet known how many organizations have been hit by demands that they pay a ransom in order to get their systems working again. But some cybersecurity researchers predict the attack targeting customers of software supplier Kaseya could be one of the broadest ransomware attacks on record.

It follows a scourge of headline-grabbing attacks over recent months that have been a source of diplomatic tension between U.S. President Joe Biden and Russian President Vladimir Putin over whether Russia has become a safe haven for cybercriminal gangs.