Cloudbleed is the name of a major security breach from the internet company, Cloudflare. Cloudflare is an optimization service that allows for quick web page loading and is used by about 3,400 websites. Over the last few months, Cloudflare accidentally leaked user passwords and other potentially sensitive information from websites using their service.
If you have an account at any of the affected sites, you should change your password as soon as possible. Some of the more popular sites affected by the leak are:
Here is a website where you can specifically check other websites that
you may be concerned about: http://www.doesitusecloudflare.com
It's probably not necessary to change all your passwords on all your Internet accounts, but if you are one of those people who uses the same password for multiple sites, it would be a good idea to change each of them to a unique password, now.
Heartbleed is just another not-so-gentle warning that you should be using a password manager and two-factor authentication. If you need help finding or using a password manager, or settings