Security researcher Troy Hunt set up Have I Been Pwned? so that people can check if their personal information has been compromised in a data breach. Hunt’s database includes hundreds of millions of leaked accounts from years of hacks from across the globe. Type in your username or email address and the site will tell you if you’ve been pwned (i.e. if your username/email has been part of a data breach).
As well as finding out if your data was leaked when say, Sony or Dropbox was hacked, you can sign up and get immediate notification if your email address or username show up in any future data breaches.
Bear in mind though, that the service isn’t 100% reliable. Many breaches are not made public and might possibly contain your information.
You can’t help it if your data ends up in a breach, but always use a strong password, try not to give your address / phone number information to a site unless you really have to, and try to use temporary email addresses and usernames where possible.
"Sometimes, no matter how well you protect your personal data, companies entrusted with keeping it safe are hacked. This is particularly frustrating because the breach is in no way your own fault. Luckily, there's a service that allows you to check if your information has been compromised. I recommend Have I Been Pwned? to absolutely everybody. It's a vital service." Jake Davis, Head of Hacking, SPYSCAPE