If someone phones me claiming to be from a particular company etc., I always ask them to prove it. For instance, a guy phoned me claiming to be from British Gas. I asked him to prove it. He said he could if I provided my security password. Eh?! Hang on! It should work the other way round shouldn't it? You tell me what password is on my account, and I'll tell you if it's correct. If I phone your company, I will tell you what my password is. It's clear that many companys' don't expect this response from people because they have to hang up when challenged. A genuine police officer will tell you what his service number is.