Documents linked with law enforcement inquiries appear to have been stolen in recent phishing attacks on certain employee email accounts, Microsoft said.
The technology giant said earlier this month that a small number of Microsoft employee social media and email accounts had been affected in a phishing attack. The accounts were reset and no customer information was compromised, Microsoft said.
On Friday, Adrienne Hall, general manager in Microsoft's Trustworthy Computing Group, said in a blog post that it appeared that documents associated with law enforcement inquiries were stolen. "If we find that customer information related to those requests has been compromised, we will take appropriate action," Hall said.
The company will, however, not comment on the validity of any stolen emails or documents in deference to "the privacy of our employees and customers -- as well as the sensitivity of law enforcement inquiries," she added.
Microsoft said its investigation continues, and that the type of attack was not uncommon, as many companies face phishing attempts from cybercriminals.
The company has been recently targeted by the Syrian Electronic Army, a hacker group that supports the Syrian regime of Bashar al-Assad. SEA attacked this month the social media properties of Skype and other Microsoft social media and blogs, including the Microsoft Office Blogs site.
In a message on Twitter, SEA accused Microsoft of selling customer data to governments, which was probably a reference to disclosures last year by former U.S. National Security Agency contractor Edward Snowden that Internet companies were allegedly providing access to real-time customer data to the agency.
Microsoft receives requests for customer data from law enforcement agencies around the world relating to Microsoft online and cloud services. Some of these are covered under "gag orders," which do not allow the company to disclose to the public the existence of the specific requests.
In March last year it started publishing its Law Enforcement Requests Report, which listed the total number of requests it receives from law enforcement agencies in countries around the world and the number of potentially affected accounts identified in those requests.
Microsoft, Google and some other Internet companies have asked the Foreign Intelligence Surveillance Court for permission to provide aggregate data on security information requests under the Foreign Intelligence Surveillance Act, which they are currently disallowed.