Drupal security advisory DRUPAL-SA-2006-026: A malicious user may entice users to visit a specially crafted URL that may result in the redirection of Drupal form submission to a third-party site. A user visiting the user registration page via such a url, for example, will submit all data, such as his/her e-mail address, but also possible private profile data, to a third-party site.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/51211/DRUPAL-SA-2006-026.txt
Source: https://packetstormsecurity.com/files/51211/DRUPAL-SA-2006-026.txt.html