MessageLabs Inc., which scans E-mail for viruses, said that within 24 hours it had scanned more than 1 million copies of the "F" variant of the "Sobig" virus, which was blamed for computer disruptions at businesses, colleges, and other institutions worldwide.
The previous record was "Klez," with about 250,000 copies spotted during its first 24 hours earlier this year, MessageLabs chief technology officer Mark Sunner said Thursday.
There have been faster outbreaks on the Internet, but those circulated through networking functions built into Windows operating systems.
The "Slammer" worm struck more than 75,000 computers in just 10 minutes in January, the number of infected computers doubling every 8.5 seconds, according to researchers at the University of California and other institutions. It went on to infect hundreds of thousands more.
E-mail viruses like "Sobig" can hit the same computer multiple times, so the number of infections are not directly comparable.
Sunner said the latest virus was able to spread so quickly because it essentially had E-mail software built-in. Previous ones relied on existing software packages like Microsoft's Outlook and did not spread as quickly among users of rival E-mail software.
Sobig began appearing Tuesday, just a week after a separate virus, "Blaster," wreaked havoc on computer systems across the world.
Sobig does not physically damage computers, files, or critical data, but it tied up computer and networking resources, forcing networks like the University of Wisconsin-Madison to shut down outside access to its E-mail system Wednesday.
"We were removing 30,000 bad E-mails an hour," said Jeff Savoy, an information security officer at the school.
In India's high-tech city of Bangalore, dozens of cybercafes shut down and home computers blacked out. Some cafes were hit because their service provider was affected, but others got the virus in their machines using Windows operating systems.
"Our cybercafe has been down since Tuesday night," said Afar, a cafe manager in north Bangalore who goes by a single name. "Customers are returning home disappointed."
The owner of one of the Internet's most popular E-mail lists, technologist David Farber, was livid about Sobig.
"I got 1,300 junk E-mails 'delivered' this AM," he said in a message to subscribers Thursday. "Find the person and put him/her in jail."