This year a lot of big name companies have had their databases hacked. A recent example of this is the Sony hacking that caused them to shut down their network till they could be certain it was re-secured.
I have even gotten letters in the mail from my credit card company and bank that there was a data breach and that I would be wise to change my user information. So after a data breach happens, what do you do? Well you could change every login and password that you have on the internet, but for me that is not practical.
Instead, you can visit Should I Change My Password, and then type in your e-mail address and it will check the database to see if your e-mail address has been compromised. If it has simply change your password, and if you want to be extra careful change the security questions as well.
If you want to learn more about the database and where it comes from check out the About page. It explains exactly where it comes from and how you should use it. The Sources page will show the databases that are included in this search engine.
The FAQ, I feel is a must visit part of the site. It will answer all the questions you may have and explains why it is safe to check to see if your account has been compromised.
The best way to keep your passwords safe is to change them often and not use them in multiple places. But most people use the same password and username for everything, so it is good to be able to check if you were compromised.