The Melissa Word 97 Macro virus, discovered late last week, has spread faster than any other virus so far found online.
According to anti-virus companies, Melissa, which spreads by emailing itself automatically from one user to another from within a Word document, spread rapidly within only hours of its release.
The virus was discovered latest Friday European time, early morning US time. According to US anti-virus company Data Fellows, many multinational companies reported widespread infections, including Microsoft and Intel.
In fact Microsoft closed down its entire email system for a time to prevent further spreading of the virus. So far, said a Data Fellows spokesperson, the number of infected PCs is believed to be in the tens of thousands and rising quickly.
Mikko Hyponnen, anti-virus research manager at the company, commented: "We've never seen a virus spread so quickly."
"We've seen a handful of viruses that distribute themselves automatically over email, but not one of them has been as successful as Melissa in the real world. When a big company gets infected, their email servers are seriously slowed down and might even crash, as people start to email large document attachments without realising it," he warned.
Other vendors agreed. Kevin Street, technical director at Symantec commented: "It's been really busy today. It's the smaller companies which will be worst affected as many do not have staff to monitor this type of issue."
He said that so far none of the anti-virus companies have any idea who wrote the virus.
"We know it came from an alt.sex newsgroup. Virus writers usually leave some sort of trademark, which gives clues to who they are. All the companies' researchers work together on this sort of thing in conjunction with law enforcement agencies and if they know anything, they are keeping it pretty quiet," he said.
Jan Hruska, technical director at Sophos, said he had received several calls about the virus yesterday.
"Its spreading so quickly because it emails itself to 50 addresses in the email file in Outlook. This could even be 50 groups of people," he warned.
He added, "It takes advantage of the features in Word 97. The whole set of features [of W97] has been put together regardless of what security problems could be caused. Anti-virus companies can only act like firefighters."
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