On Friday night, Microsoft sent notification emails to an unknown number of its individual email users—across Outlook, MSN, and Hotmail—warning them about a data breach. Between January 1 and March 28 of this year, hackers used a set of stolen credentials for a Microsoft customer support platform to access account data like email addresses in messages, message subject lines, and folder names inside accounts. By Sunday, it acknowledged that the problem was actually much worse.

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