On his CodingHorror blog, Jeff Attwood quotes a story forwarded to him that describes how a user discovered that a shareware tool G-Archiver, that backs up Gmail accounts was secretly emailing each user’s Gmail usernames and passwords to its creator own personal Gmail account. On discovering this the person logged into the author’s Gmail account using the author’s username and password embedded in the utility and found in its mailbox, 1,777 emails with Gmail account information of people who used the software. The user deleted these messages and then changed the account’s password to stop the author from seeing any more emails with account information and contacted Google.
Collecting the Gmail usernames and passwords of the people who used your tool is surely illegal. I hope this gets investigated by the police.