Have you been Pwned? (Password Stolen)
Security Researcher Troy Hunt has set up a website, https://haveibeenpwned.com/ which enables people to check if their details are on any leaked or hacked password/information lists.
I strongly recommend everyone try all of their emails. This site is safe and only looks up your email, it does not ask you for a password.
If you are on any of the lists containing passwords, its time to update some passwords.