BT Yahoo!
I believe there was a thread running here about a change to BT Yahoo! mail and a possible scam with fake adverts etc. but I can't find it.
Today I had a mail in my Spam folder that appeared to be from BT notifying me of an upgrade and to click here or I won't be able to use BT mail after 27 Sept. It certainly looked like it was from BT but three things. It was in my spam folder, and images were blocked. These images were the BT and Yahoo logos.
The other thing was that it was sent to a sub-account and not to my main account. This particular sub-account is the one I use most often.
I know this has been covered before and perhaps someone could provide a relevant link. Cheers.