DigiNotar breach (2011)
In July 2011, attackers breached Dutch certificate authority DigiNotar and issued fraudulent certificates for Google, Yahoo, Mozilla, and Tor. The breach went undetected for over a month.
Browser makers revoked trust in DigiNotar within days. The company filed for bankruptcy in September 2011.
The incident led to stricter CA oversight and helped drive the development of certificate transparency.
Shows the consequences of a compromised CA: browsers revoke trust, and the CA often collapses.
