Do you use Gravatar to display a custom image next to your comments on various blogs? Or do you have a blog at wordpress.com? If so, Gravatar has your email address, and it might be easy for a hacker to figure out what that address is.

Wordfence explains the problem, and why it matters.

For example: A user may be comfortable having their full name and profile photo appear on a website about skiing. But they may not want their name or identity exposed to the public on a website specializing in a medical condition. Someone researching this individual could extract their Gravatar hash from the skiing website along with their full name. They could then Google the hash and determine that the individual suffers from a medical condition they wanted to keep private. [continue]