McAfee Inc. confirmed that a software update it posted at 9 a.m. Eastern time caused its antivirus program for corporate customers to misidentify a harmless file. It has posted a replacement update for download.
"We are not aware of significant impact on consumers and believe we have effectively limited such occurrence," the company said in a statement.
Online posters begged to differ, saying thousands of computers running Windows XP with Service Pack 3 were rendered useless.
About a third of the hospitals in Rhode Island were forced to stop treating patients without traumas in emergency rooms. The hospitals also postponed some elective surgeries, said Nancy Jean, a spokeswoman for the Lifespan system of hospitals. The system includes Rhode Island Hospital, the state's largest, and Newport Hospital, the only hospital on Aquidneck Island.
Jean said patients who required emergency care for gunshot wounds, car accidents, blunt trauma and other potentially fatal injuries were still being admitted to the emergency rooms.
In Kentucky, state police were told to shut down the computers in their patrol cars as technicians tried to fix the problem. The National Science Foundation headquarters in Arlington, Va., also lost computer access.
Peter Juvinall, systems administrator at Illinois State University in Normal, said that when the first computer started rebooting it quickly became evident that it was a major problem, affecting dozens of computers at the College of Business alone.
"I originally thought it was a virus," he said. When the tech support people concluded McAfee's update was to blame, they stopped further downloads of the faulty software update and started shuttling from computer to computer to get them working again.
Such personal attention to each PC from a technician appeared to be the only way to fix the problem because the computers weren't receptive to remote software updates when stuck in the reboot cycle. That slowed the recovery.
Intel Corp. appeared to be among the victims, according to employee posts on Twitter. Intel did not immediately return calls for comment.