Microsoft has extended two-factor authentication to all Office 365 users, giving an optional second layer of protection against attacks.
Subscribers to Microsoft's midsize business, enterprise, academic, non-profit and individual Office 365 plans can enable two-factor authentication for free, the company said.
Previously, the feature was only available to Office 365 admins.
With the new feature, users will have to use a second mode of verification on top of their password, such as taking a phone call or entering a code sent via text or the Office 365 app.
"Multi-factor authentication increases the security of user logins for cloud services above and beyond just a password," said Paul Andrew, a technical product manager for Office 365.
"With multi-factor authentication for Office 365, users are required to acknowledge a phone call, text message, or an app notification on their smartphone after correctly entering their password," he added. "Only after this second authentication factor has been satisfied can a user sign in."
Microsoft said it plans to extend the feature to desktop apps including Outlook, Lync, Word, Excel, PowerPoint, PowerShell, and OneDrive for Business later this year.