On Thursday July 12th some 450,000 usernames and unencrypted passwords of Yahoo! Voice users were leaked on the internet. You can use this tool to lookup email addresses from the list. You cannot lookup passwords or list the email addresses with this tool.
AfterDawn.com doesn't have a role in the leak. We merely provide this search as a service to our users and concerned consumers. Neither do we have a record of the passwords - only the email addresses that are indexed for search purposes.
The search looks for partial matches and full matches of addresses.