Many HTTPS-secured sites on the internet use OpenSSL. Unfortunately, a major vulnerability in OpenSSL was disclosed - known as the Heartbleed bug - yesterday that put hundreds of thousands of servers at risk of compromise.
Whilst some servers have been patched already, many remain that have not been patched. Chromebleed uses a web service developed by Filippo Valsorda and checks the URL of the page you have just loaded. If it is affected by Heartbleed, then a Chrome notification will be displayed. It's as simple as that!
Please note that, in some jurisdictions, site testing can only be carried out with the express permission of the site owner. Please check what the law says in your local area before proceeding to download this extension.