PhoneFactor is a multi-factor authentication system which utilizes phone calls to verify identity. With multiple out-of-band methods (phone call, text message, and push) and an OAUTH passcode option, PhoneFactor provides flexibility for users and a single multi-factor platform for IT to manage.
PhoneFactor was founded as Positive Networks Inc. in 2001 by Tim Sutton and Steve Dispensa. The PhoneFactor product was launched by Positive Networks in 2007, and the company changed their name to PhoneFactor Inc. in 2009.  On October 4, 2012, Microsoft acquired PhoneFactor, and the PhoneFactor service is now available as Azure Multi-Factor Authentication. In addition to securing on-premises applications and identities, the service now also works with cloud applications like Office 365 that use Windows Azure Active Directory.
- Haiyang Qian; Chandra S. Surapaneni; Steve Dispensa; Deep Medhi (June 2009). Service Management Architecture and System Capacity Design for PhoneFactor--A Two-Factor Authentication Service (PDF). IFIP/IEEE International Symposium on Integrated Network Management (IM'2009). Archived from the original (PDF) on 2013-09-27.
- Haiyang Qian; Chandra S. Surapaneni; Marsh Ray; Steve Dispensa; Deep Medhi (April 2010). DReaM-Cache: Distributed Real-Time Transaction Memory Cache to Support Two-Factor Authentication Services and its Reliability (PDF). IEEE/IFIP Network Operations and Management Symposium (NOMS'2010). Archived from the original (PDF) on 2013-09-27.
- "PhoneFactor Product Review". SC Magazine.
- "Positive Networks changes name to PhoneFactor". Kansas City Business Journal. bizjournals.com. 7 January 2009. Retrieved 11 July 2018.
- "Two-Factor Authentication Without Tokens: Positive Networks Debuts PhoneFactor(TM)" (Press release). Business Wire. 22 May 2007. Retrieved 11 July 2018.
- Quain, John R. (8 Oct 2008). "Logging on Securely, and Confirmed via a Cellphone Call as a Sentinel Against Intruders". New York Times / NYT.com.
- "Microsoft buys security vendor PhoneFactor". Computerworld. 4 Oct 2012.