The Heartbleed Bug is probably the most serious menace to the modern Internet, a serious flaw in the popular OpenSSL library that is having a great impact. Security experts have analyzed all websites which use SSL distinguishing vulnerable from safe, nearly 5% are affected by the flaw (CVE-2014-0160) The flaw allows an attacker to reveal up to 64kB of memory to a connected client or server. The flaw could have exposed users sensitive account information over the past two years.”]
Source: http://securityaffairs.co/wordpress/23878/intelligence/statistics-impact-heartbleed.html