Trustworthy Computing Security general manager Matt Thomlinson said it experienced a similar security intrusion to the internet giants.
"Consistent with our security response practices, we chose not to make a statement during the initial information gathering process," Thomlinson said in a statement.
"During our investigation, we found a small number of computers, including some in our Mac business unit, that were infected by malicious software using techniques similar to those documented by other organisations. We have no evidence of customer data being affected and our investigation is ongoing.”
The incident is similar to a compromise of Facebook and Apple computers which were targeted in a sophisticated attack when some employees visited an exploit-laden mobile developer website.
Web development site iPhoneDevSDK shouldered the responsibility for the Facebook compromise. Administrator Ian Sefferman said it was alerted to the fact that its site was "part of an elaborate and sophisticated attack whose victims included large internet companies" and prior to media attention, it had no knowledge of the breach and hadn't been contacted by Facebook, any other company, or any law enforcement about the potential breach.
Thomlinson said: “This type of cyber attack is no surprise to Microsoft and other companies that must grapple with determined and persistent adversaries. We continually re-evaluate our security posture and deploy additional people, processes and technologies as necessary to help prevent future unauthorised access to our networks.”