The Heartbleed Bug is a serious flaw in the popular OpenSSL library that allows an attacker to reveal up to 64kB of memory to a connected client or server. The library is present in a wide variety of OSs as well as applications and most popular web servers including Nginx and Apache. CloudFlare already implemented its own fix for the OpenSSL vulnerability last week. The bug was introduced to OpenSSL in December 2011 and has been out in the wild since OpenSSL release 1.0.1g released on 7th of April 2014.”]
Source: http://securityaffairs.co/wordpress/23808/hacking/heartbleed-bug-openssl.html