the website is visited unless the user manually marks the website's certificate as trusted. Because unencrypted websites do not currently display any such warnings, the use of self-signed certificates is not well received. In 2015, Mozilla started to roll out opportunistic encryption in Firefox version 37. This was quickly rolled back (in update 37.0.1) due to a serious vulnerability that could bypass SSL certificate verification. Browser extensions like HTTPS Everywhere and HTTPSfinder find and automatically switch the connection to HTTPS when possible. Several proposals were available for true, seamless opportunistic encryption of HTTP/2 protocol. These proposals were later rejected. Poul-Henning Kamp, lead developer of Varnish and a senior FreeBSD kernel developer, has criticized the IETF for following a particular political agenda with HTTP/2 for not implementing opportunistic encryption in the standard. Weaknesses STARTTLS implementations often used with SMTP are vulnerable to STRIPTLS attacks when subject to active wiretapping. See also John Gilmore Multi-factor authentication Opportunistic TLS Opportunistic Wireless Encryption (OWE) Security level Security level management tcpcrypt References External links Enabling Email Confidentiality through the use of Opportunistic Encryption by Simson Garfinkel of the MIT Laboratory for Computer Science, May 2003 Windows KB article on NAT-T and DH2048 – Opportunistic Encryption using the Internet Key Exchange (IKE) – Pervasive Monitoring Is an Attack Cryptographic software Internet Protocol based network software Internet privacy