I got that email too, via Outlook . I was immediately suspicious because a link took you to the BTYahoo log in frame. I'm not sure that BT or Yahoo would send you emails asking for you to use your log in details. That is bad practice.
To be sure I logged in via my usual method by going to the BtYahoo site myself. There was absolutely no sign of any upgrade requirement. This pretty well confirmed to me that this was a sophisticated Phishing attempt. So, I forward the email to Yahoo's phishing department.
If you logged on using the email link I would advise you to change your password pronto!
Virgin Media: 100mb/10Mb , land line, mobiles x2, TV - VIP HD box + TIVO 1Tb box.
Edited by roughbeast (Thu 25-Apr-13 09:40:26)