Send login link in email to registered users On my Drupal 6 website, there are around 400 users registered by site admin and none of then know that they are registered on the site. Now I want to increase the number of registered users but in a secure manner.

I want the registered users to be able to invite at most 5 people whom they think are the most eligible. This is very easy and has been done. 

The problem is that to invite new users, the current users will need to login and I dont want them to know their username and password as they will be given to them later. 

So the only solution that remains is that I send them a login link in their e-mail so that they can click on the link and get automatically logged in so they can invite 5 other people of their choice.
You should be able to use the Login one time module for this.


  Login one time provides the ability to email one-time login links to
  users. You can also choose the pages they will land on.


I would imagine that the users might be able to change their own paswords after using this one time link.  To prevent this, you should be able to use the Edit own user account permission module.


  This module manage edit permissions to the name, mail and password
  profile filed. You can manage permissions to the other profile
  entities by other admin menu settings.