Many web sites are not properly secured, you can use google search to find private data, including user name, passwords or even full database backups. Some scripts used to backup database just dump database to public folders, which any one can access resulting security problems.

Following site have lot of ways to find these info with google search.

http://johnny.ihackstuff.com/ghdb.php

Hacking is evil. Don’t do it. If you do it, one day you will also get hacked. Only use the knowledge for good things, not to create problem for others.