Have I Been Pwned is a service that shows any data breaches that contain the specified email address or account name. It can be a great reminder for the need to use unique passwords across all web services, as once a particular email/password or username/password combination is compromised, attackers will use automatic wordlists with those combinations to attempt to gain access to accounts on other websites or services as well.

Give it a shot below, and see how many breaches you've been affected by.