To avoid registrations by spambots, you need to give know a “secret word” to create a new account. If you've been invited to join the PET project, you should have been given this “secret word” by the person who invited you.
If you have not been invited, but still want to join, you're most welcome! Just Contact me and tell me why you are interested in the project and want to join, and I shall email you the secret word.
