@hc4361
Thanks for explaining. A worrying state of affairs although, the minute I saw "let FB access your email address book" my reaction was "no (expletive) way". People who gave me their email addresses did so *in confidence* and I have no business letting a third party organisation get hold of it.
Your scenario was, I duspect, exaggerated for effect
//So if the dentist's receptionist uses the dentist's email address to create an email account it is possible that all of the patients email addresses can be accessed by FB and send these 'people you may know' messages.
//
indeed, the above example would put the dentist in breach of the data protection act (in UK). A sensible IT setup would, of course block employees from making any such security blunders. Staff with no cause to generate or receive email shouldn't even be able to run the Outlook/Live Mail software required to read it. Then again, there's webmail and blocking the web browser would be a bit draconian unless it really is an inappropriate timewaster in the context of many job types.
Anyway, we know Facebook is one of many user-data wh*res online: it's the core of their business model. It's just depressing that, no matter how careful I am about my friends' e-addresses, I only need one careless friend for me to end up in some marketing database or some spammer's list.