In a blog post, Scott Charney, vice president of Microsoft's Trustworthy Computing Group, said the company will take the additional step of warning users when they have been "targeted or compromised by an individual or group working on behalf of a nation state." Microsoft already warns users if their account information has been targeted or compromised by a third party.
Popular Microsoft accounts include Outlook.com and OneDrive.
"We’re taking this additional step of specifically letting you know if we have evidence that the attacker may be 'state-sponsored' because it is likely that the attack could be more sophisticated or more sustained than attacks from cybercriminals and others," Charney wrote. "These notifications do not mean that Microsoft’s own systems have in any way been compromised."
The move comes after Reuters said it first asked Microsoft why the company did not tell customers about an alleged Chinese state-sponsored hack from May 2011.
Microsoft said in a statement today "neither Microsoft nor the U.S. Government were able to identify the source of the attacks, which did not come from any single country."
"Our focus is on helping customers keep personal information secure and private. Our primary concern was ensuring that our customers quickly took practical steps to secure their accounts, including by forcing a password reset," a company representative said in a statement.
"As the threat landscape has evolved our approach has too, and we’ll now go beyond notification and guidance to specify if we reasonably believe the attacker is 'state-sponsored,'" the statement said.
ABC News' David Rind contributed to this report