Microsoft has admitted to being hit in a recent string of high-profile hacking operations.
The company said that it was among the firms to have staff machines compromised as the the result of a hacking operation which also ensnared employees of Apple, Facebook and Twitter. No customer data is believed to have been lifted.
The infections are believed to be the result of a "watering hole" operation in which a popular iOS developer site was compromised and pages were equipped with a series of exploit scripts which then installed malware.
By targeting a specialised developer site, the attackers were able to attract high-value targets such as Apple, Twitter and Microsoft employees. Redmond said that the infected systems belonged to members of its Mac business unit.
"This type of cyberattack is no surprise to Microsoft and other companies that must grapple with determined and persistent adversaries," said Microsoft Trustworthy Computing general manager Matt Thomlinson.
"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."
Microsoft's disclosure was made late Friday US Pacific time, days after Apple, Twitter and Facebook were named as victims. The company said that the timing was a result of due diligence rather than an effort to minimise impact.
"Consistent with our security response practices, we chose not to make a statement during the initial information gathering process," said Thomlinson.
"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."
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