After spending hours ridding their networks of a nasty computer worm, most corporations managed to stave off an attack by “Kama Sutra” that was expected to delete all files from users’ machines, antivirus firms said Friday.

The worm, which goes by many other names including Blackworm, Blackmail, Grew, Nyxem, and MyWife, has been rated as a low-to-medium risk by security companies (see Worm Readies Massive Attack).

Antivirus companies said there have been few reports of havoc caused by the worm because most users were aware of the impending attack and prepared their machines in time to avert disaster.

After infecting computers earlier in the week through email attachments, the worm was set to activate when users turned on their computers Friday. It was feared it would wipe out all files including Microsoft Word documents, PDF files, Excel Worksheets, and photos.

“The actual impact of the worm has been almost negligible,” said Shane Coursen, senior technical consultant for Kaspersky Lab, an antivirus company. “The media attention given to this worm has been huge and it helped get the message out to most users.”

On Thursday, security company Symantec estimated that about 300,000 machines would be infected. Antivirus maker Trend Micro said it received reports of infection from 27,000 computers, and expected to see reports from a few thousand more users.

Although a sizable number of machines have been infected, there are very few reports of mayhem caused by the worm.

There were reports of damage caused to a few thousand computers in India, said the Internet Storm Center at the SANS Institute, a computer security training and certification company.

Early Detection Helps

One reason the worm caused only modest harm could be the early detection of the cyber critter by antivirus companies. Most security companies developed an antidote to the worm nearly two weeks ago and were talking about it publicly to raise awareness.

The response was different from some of the recent worm attacks including the Zotob worm, which had a dramatic effect on users in less than five days after Microsoft disclosed the security vulnerability and released a patch for the worm.

The short window between the release of the patch and the spread of the worm caused many computers to become infected (see Zotob Cost $97K per Company).

But the latest worm was different. “We were able to receive a sample of the worm early so we could analyze the worm much in advance,” said Mr. Coursen.

Kaspersky Lab said it issued an alert for the worm on January 16.