The blogger then send a screenshot of the Windows operating system has not been released on his blog.
To find out the source of the leak, Microsoft began an investigation and, as part of that search, look at the accounts of bloggers to find out the name of the employee.
The search was legal because it falls on the state services that companies can access account information stored on "Communication Services" of his, including email, chat areas , forums, and other media from Microsoft.
On Thursday, the company acknowledged the anonymous blogger's email read to determine an employee suspected of leaking information.
Microsoft owns Hotmail, a free email service called Outlook.com now.
John Frank, Microsoft's deputy general manager, said it was "extraordinary action in this case."
While the search is technically legal, he said Microsoft will consult with external consultants in the future.
Microsoft's actions came to light this week as part of a legal case by US prosecutors against former employees of Microsoft, Alex Kibalko, a Russian native who is based in documents Lebanon corporate rooms.
The terms of service added: "Microsoft has the right to review materials posted to the Communication Services and to remove any materials in its sole discretion."
However, disclosure of the search has led to renewed focus on the violations of the privacy of technology companies.
It has also left Microsoft in a quandary, as the company often criticized rival Google to automatically scan the user's email it to serve them with ads.
Microsoft is caught up in a privacy storm after admitting it read a blogger's Hotmail mailbox while pursuing an investigation into the leaked software.
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