Philip R. Zimmermann is the creator of Pretty Good Privacy, an email encryption software package. Originally designed as a human rights tool, PGP was published for free on the Internet in 1991 and became the most widely used email encryption software in the world. In early 1996, Zimmermann founded PGP Inc. That company was acquired by Network Associates Inc (NAI) in 1997, where he stayed on for three years as Senior Fellow. In 2002 PGP was acquired from NAI by a new company called PGP Corporation, where Zimmermann served as special advisor and consultant until its acquisition by Symantec in 2010. Zimmermann currently is consulting for a number of companies and industry organizations on matters cryptographic. He served as a Fellow at the Stanford Law School's Center for Internet and Society. He was a principal designer of the cryptographic key agreement protocol for the Wireless USB standard. Since 2004, his focus has been on secure telephony for the Internet, developing the ZRTP protocol and creating products that use it, including Zfone. Zimmermann's new startup is Silent Circle, a provider of secure communications services.