Find out if your password has been pwned

To Pwn is a slang term derived from the verb own, meaning to appropriate or to conquer to gain ownership of an online account or server, website, router or application. It is synonymous hacking or cracking.

The "haveibeenpwned" website has collected over half a billion real-world passwords previously exposed in data breaches.  They're searchable online below as well as being downloadable for use in another online system.

Here are the two most relevant research options:

When you find out that your email address or password has been found on a pwned website since the last time you updated the password on this website you have to change your password.  If you have been using the same password across other websites, you have to change it on all of them. At this time it's time to finally start using a good password manager like  "1Password" or "LastPass". While at it, enable the 2 step verification wherever available.