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Russian citizen Andrey Sabelnikov "wrote and/or participated in creating" the harmful software which infected thousands of machines, Microsoft said.
Kelihos was used for sending out spam and spreading malware until it was "neutralised" in September 2011.
Microsoft said Mr Sabelnikov is currently working on a freelance basis with a software development and consulting firm.
Prior to this, Mr Sabelnikov is said to have worked as a software engineer and project manager at "a company that provided firewall, antivirus and security software".
Microsoft did not name the company - however Mr Sabelnikov's LinkedIn profile lists St Petersburg-based antivirus firm Agnitum among Mr Sabelnikov's former employers.
Agnitum's sales and marketing director Vitaliy Yanko told the BBC: "I have checked the info and may confirm that Andrey Sabelnikov worked at Agnitum from 2005 till 2008.
"Afterwards our ways parted. Seems that he chose the wrong route afterwards."
Create the problem - provide the solution - get rich.