Found the answer, thanks for the replies chaps.
A good way to stop anyone e-mailing from your address book is to create a new contact and call it 0 AAAAA [that's zero space AAAAA]; this should make it the first entry in you address book. Do not enter an e-mail address. When the nasty tries to add it, it generates an error message and won't progress further until it gets an input from you.