Former certificate authorities

American software company

Verisign, Inc. is an American company based in Reston, Virginia, that operates a diverse array of network infrastructure, including two of the Internet's thirteen root nameservers, the authoritative registry for the , , and generic top-level domains and the country-code top-level domains, and the back-end systems for the and sponsored top-level domains.

Equifax Inc. is an American multinational consumer credit reporting agency headquartered in Atlanta, Georgia and is one of the three largest consumer credit reporting agencies, along with Experian and TransUnion (together known as the "Big Three"). Equifax collects and aggregates information on more than 800 million individual consumers and more than 88 million businesses worldwide. In addition to credit and demographic data and services to business, Equifax sells credit monitoring and fraud prevention services directly to consumers.

American computer and network security company

Thawte Consulting (pronounced "thought") is a certificate authority (CA) for X.509 certificates. Thawte was founded in 1995 by Mark Shuttleworth in South Africa. As of December 30, 2016, its then-parent company, Symantec Group, was collectively the third largest public CA on the Internet with 17.2% market share.

GeoTrust is a digital certificate provider. The GeoTrust brand was bought by Symantec from Verisign in 2010, but agreed to sell the certificate business (including GeoTrust) in August 2017 to private equity and growth capital firm Thoma Bravo LLC. GeoTrust was the first certificate authority to use the domain-validated certificate method which accounts for 70 percent of all SSL certificates on the Internet. By 2006, GeoTrust was the 2nd largest certificate authority in the world with 26.7 percent market share according to independent survey company Netcraft.

StartCom was a certificate authority founded in Eilat, Israel, and later based in Beijing, China, that had three main activities: StartCom Enterprise Linux (Linux distribution), StartSSL (certificate authority) and MediaHost (web hosting). StartCom set up branch offices in China, Hong Kong, the United Kingdom and Spain. Due to multiple faults on the company's end, all StartCom certificates were removed from Mozilla Firefox in October 2016 and Google Chrome in March 2017, including certificates previously issued, with similar removals from other browsers expected to follow.