The Heartbleed bug is a flaw in OpenSSL encryption software that could allow hackers to access data on secure servers, including credit card or bank details, passwords and other sensitive personal information. It was originally discovered in April 2014, and it could affect upward of 500,000 websites.
OpenSSL is open-source software that is one of the most widely used online encryption standards, used by such websites as Facebook, Gmail, Yahoo, Amazon, OKCupid and many more. It is also what many companies use for securing their internal servers, which means the Heartbleed bug could potentially allow hackers to access private company data by intercepting the server's security keys.
The Heartbleed bug is a very serious risk as more than 81 percent of servers run on software that uses OpenSSL. Only OpenSSL versions 1.0.1 through 1.0.1f are affected by this security flaw, but this means that a huge proportion of supposedly secure information sent since 2012 could have been stolen.
Since the virus was first discovered, many major websites, such as Facebook, Netflix, eBay and Instagram, have taken steps to upgrade their encryption software to fix the flaw. However, experts think it may take all sites to upgrade their encryption software to eliminate the bug fully.