Neowin.net reported the alleged leak that was posted last week on a site commonly used by web developers to share code.
The information has since been removed from the website where it was posted. It is presently unclear how the login information was acquired.
According to Newowin.net, the accounts were largely registered in Europe. It is likely the information was gathered in phishing scams, in which victims are invited by fake web pages or emails to provide account information.
Microsoft is investigating the reports and it is currently unclear what accounts were compromised.