Microsoft is offering rewards of $500,000 (£300,000) for information leading to the arrest of the hackers responsible for the MSBlast and SoBig viruses.
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The Blaster-A worm, which exploited a security hole in Microsoft Windows, and the Sobig-F worm, cost businesses millions of pounds when they struck in August this year.
Microsoft has teamed up with the FBI and the US Security Service, in an attempt to coax the hacker community into blowing the whistle on the virus authors.
The Sobig-F and Blaster-A viruses damaged Microsoft’s credibility and dented its profits by $700m.
"There must be people out there in the computer underground who know who is responsible for the creation of these malicious worms. Offering a total of $500,000 will be a great temptation for someone to break their silence," said antivirus specialist Sophos.
The FBI arrested Jeffrey Lee Parson in August and Dan Dumitru Ciobanu was charged in Romania, after writing variants of the Blaster worm.
The perpetrators of the original worm have not yet been caught.