Heartbleed bug is a vulnerability in OpenSSL that came to light in April of 2014. It was present on thousands of web servers, including those running major sites like Yahoo. The vulnerability meant that a malicious user could easily trick a vulnerable web server into sending sensitive information, including usernames and passwords. OpenSSL is an open source code library that implemented the Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols. When the bug was made public, it affected 17% of all SSL servers.”]