This plug-in really works, but I feel a little uncomfortable because it always ask the same card... if someone sees/ records the combination even one time, in theory they can update the login page until they get the challenge that they want... and login.
The other problem is that for whatever the reason it works for some e-mails and not for others.
The other problem is that sending passwords to e-mail is not really that secure!
Any extra security is welcomed, and better than nothing! But after using it I felt compelled to search another that provide much better protection, and I think "Perfect Paper Passwords" plug-in is much better for this propose.