title: Hooking into drupal's password mechanism
body: <p>I'm converting a site from a forum system (mybb) into a drupal site and obviously the password schemes are completely different.</p>
  
  <p>I'm planning on importing all of the users with their old password hashes prefixed with "mybb_".</p>
  
  <p>I'd like to write a module which detects prefixed passwords if the user logs in authenticates using the old mechanism and then replaces the password with a drupal 7 hashed password.</p>
  
  <p>I'm relatively new to drupal development so I'm not familiar enough with the hooks, etc needed to do this.</p>
  
  <p>Any guidance would be great :)</p>
  
  <p>(Also if there is a better way of dealing with this than I have proposed, please feel free to chime in.)</p>