The economic cost of the Mydoom email virus has been estimated at US$26.1bn so far, revealed a report.
The Mydoom virus, the fastest spreading virus known so far, has claimed its first corporate scalp, US software company SCO.
The report said Mydoom had left thousands of computers vulnerable to hackers by opening up security holes in computer systems.
SCO said the virus was "overwhelming the internet" with requests for its website. According to the report, experts said the Mydoom virus accounted for 30% of all email traffic at its peak.
A variant of the Mydoom virus is expected to attack Microsoft's website from Tuesday. The original version of the virus will become inactive on 12 February.
The virus, also known as Novarg or Shimgapi, emerged last Monday as a spam email message with the virus disguised within it.
Both SCO and Microsoft have offered rewards of $250,000 each for help to catch the creator of the email worm, revealed the report.
