Check if any of your email accounts have been compromised in a data breach by visiting Have I Been Pwned?
If you have been affected by a data breach, this site will tell you which one(s). In this example, the email account I checked had been part of the Adobe account hack:
Oh no — pwned on 1 site!
Adobe: The big one. In October 2013, 153 million accounts were breached with each containing an internal ID, username, email, encrypted password and a password hint in plain text. The password cryptography was poorly done and many were quickly resolved back to plain text. The unencrypted hints also disclosed much about the passwords adding further to the risk that hundreds of millions of Adobe customers already faced.
Here is a list of confirmed data breaches which have been publicly acknowledged.
Details of some breaches have not been publicly disclosed – such as the Target exploit – and aren’t included in this analysis.