Finn Contini, 36, a former group assistant with the company, was one of four ex-employees charged in November in connection with a conspiracy to obtain the software and then sell it for personal profit.
Contini pleaded guilty yesterday to charges of conspiracy to commit mail fraud and money laundering, reports the Seattle Times. He will be sentenced on 3rd June.
According to the report, Contini made $2.3 million out of the scam, but has now forfeited over $1.7 million, in part made up of properties in Oregon and Washington.
Two other conspirators, Alyson Clark, 38, and Robert Howdeshell, 40, are due in court today.
Microsoft has suffered similar thefts in the past. In June 2003 a former Project Coordinator for Windows Development, Richard Gregg, was charged with mail and computer fraud after allegedly obtaining software with a retail value of $17 million through the company's staff software purchasing system and selling it at a profit.
In December 2002, former Microsoft manager Daniel Feussner, 32, was arrested and accused of stealing $9 million worth of Microsoft software through the same internal ordering system. Mr Feussner swallowed anti-freeze shortly afterwards, and died in hospital.