Microsoft has confirmed that it's the latest among a number of high-profile technology and internet firms to have been hit by a cyber attack.
A blog posted on Friday by Microsoft security manager Matt Thomlinson revealed:
"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."
Microsoft said there's no evidence that customer information was compromised, but an investigation is ongoing.
"This type of cyber attack is no surprise to Microsoft and other companies that must grapple with determined and persistent adversaries," Thomlinson added.
The cyber attack on Microsoft follows similar attacks on Apple and Facebook, with Facebook blaming the breach on a zero-day Java exploit.
"Last month, Facebook Security discovered that our systems had been targeted in a sophisticated attack. This attack occurred when a handful of employees visited a mobile developer website that was compromised," said Facebook's security team in a blog post.
"The compromised website hosted an exploit which then allowed malware to be installed on these employee laptops. The laptops were fully-patched and running up-to-date anti-virus software. As soon as we discovered the presence of the malware, we remediated all infected machines, informed law enforcement, and began a significant investigation that continues to this day."
Facebook knew at the time that it wasn't the only victim of the attack and shared details about it with other companies. Microsoft gave its reason for not revealing the security breach sooner: "Consistent with our security response practices, we chose not to make a statement during the initial information-gathering process."
Cyber attacks have become an increasingly high profile issue in recent months, with US security research firm Madriant Corp accusing the Chinese government of funding cyber criminals. China has denied claims it has stolen data from US firms.