Microsoft has purchased PhoneFactor, a provider of phone-based, two-factor authentication offerings, for an undisclosed amount, the companies announced on October 4.

Microsoft is pitching the deal as helping the company provide "a broader range of authentication services to Microsoft's cloud customers." But the PhoneFactor technology also can be used to help secure on-premises products, such as SharePoint running on an in-house server, as well.

PhoneFactor already works with many Microsoft products and services, including Outlook Web Access and Internet Information Services, and interoperates with Active Directory, according to the Overland Park, Kansas-based company.

Phone Factor is commiting to continue to sell its line-up of existing products. It also plans to further integrate with Microsoft's Active Directory, Windows Azure Active Directory (the cloud complement to Microsoft's on-premises directory service) and Office 365.

From Phone Factor's frequently asked questions document on the Microsoft acquisition:

"For now, we will continue to sell PhoneFactor’s solution as a standalone service using the PhoneFactor pricing model and contracts. We intend to onboard PhoneFactor into Microsoft’s programs and continue to sell it as a standalone service to our customers using Microsoft’s Volume Licensing contracts; the timing of this transition has yet to be determined."

Phone Factor's current line up includes authentication plug-ins and products for IBM Tivoli; Citrix; PingFederate; and VMWare View, among others.

The newest acronym added to the Microsoft family, as of today: MFA (multi-factor authentication).