A routine anti-virus update from Web security firm McAfee confused a valid Windows file with a virus on Wednesday, disrupting computers around the world.
Universities, hospitals and businesses across the United States were among those reporting problems after the update misidentified a valid Windows system file as malicious code and caused computers to continually reboot.
The problem hit corporate users of Microsoft's Windows XP Service Pack 3 operating system, according to McAfee, which released another update later in the day to fix the problem and urged customers to download it.
The Internet Storm Center, an initiative of the SANS Technology Institute which monitors problems on the Web, said "the affected systems will enter a reboot loop and lose all network access."
The center said it received reports of "networks with thousands of down machines and organizations who had to shut down for business until this is fixed."
The McAfee software slip "pretty much took Intel down today," said analyst Rob Enderle of Enderle Group in Silicon Valley.
Enderle told of being at the computer chip titan's headquarters in Northern California for an afternoon of meetings when laptop computers began crashing around him.
"Much of Intel was actually taken out," Enderle told AFP. "I imagine most companies running Intel and McAfee were literally taken out."
It was not immediately possible to determine how many computers had been affected around the world by the faulty update, but the number was likely to run into the tens of thousands.
McAfee for its part said "we are not aware of significant impact on consumers. We believe that this incident has impacted less than one half of one percent of our consumer base and enterprise accounts globally," it said.
Micro-blogging service Twitter was flooded with complaints by users about Santa Clara, California-based McAfee, one of the world's leading providers of anti-virus software and computer security systems.
"It is not often that a security vender takes out a large number of their clients," Enderle said. "Customers don't forget this stuff any time soon. This is going to hurt McAfee."
Among the US universities reporting problems was the University of Michigan. The website AnnArbor.com said 8,000 of the 25,000 computers in the university's health system and medical school were hit.
Syracuse, New York's Upstate University Hospital saw 2,500 of its 6,000 computers affected, the website Syracuse.com quoted a hospital spokeswoman as saying.
McAfee said "the faulty update was quickly removed from all McAfee download servers, preventing any further impact on customers" and that it was taking "measures to prevent this from reoccurring."
"We sincerely apologize for the inconvenience this has caused our customers," the company said in a statement.
A McAfee online support forum was unavailable, meanwhile, displaying a page which read: "The McAfee Community is experiencing unusually large traffic which may cause slow page loads."Reuse content