Hello,
My name is David Hubbard. I am the President/CEO of Hubbard Genesis Corporation. As a Compliance Officer for third-party credit/debit card processors I understand the security issue brought to DNN's attention. What the community failed to do was provide a solution to your original concern.
I googled "We are pleased to advise that you have been added as a Registered User" and came across this link:
http://books.google.com/books?id=L4C7cm5N9YkC&pg=PA267&lpg=PA267&dq=%22We+are+pleased+to+advise+that+you+have+been+added+as+a+Registered+User%22&source=bl&ots=zVlBeS7fO2&sig=OfkGxWOPkb7eAlWeKmalHUIwrnk&hl=en&ei=unOLSt2sE4_aNtDNuckP&sa=X&oi=book_result&ct=result&resnum=2#v=onepage&q=%22We%20are%20pleased%20to%20advise%20that%20you%20have%20been%20added%20as%20a%20Registered%20User%22&f=false
This link provide access to an online version of 'DotNetNuke for Dummies'. It explains how you can navigate to Admin>Languages>Language Editor> in order to gain access to various response templates, including the email notifications. You can edit the templates to remove elements or "mask" them, like replacing the password [Membership:Password] command with "********". This way you can send the notification to your user and make them responsible for saving their password. I also editied the password notification so it does not include the User ID.
The file you want to edit is \App_GlobalResources\GlobalResources.resx in case you wanted to manually edit the file.
It is amazing that no one at DNN was able to address this issue in a timely manner. Perhaps they did not understand the question. It may help to be more concise in the future.