There are increasing number of BT, BT Internet and Yahoo email accounts being hacked. The main source of this appears to be a phishing email with a dubious link.
The email is made to look as if it is genuinely from Yahoo! or BT. It may ask you to click on a link to upgrade or verify your account. These fake emails are quite convincing as they copy of the yahoo and BT logos.
As a precautionary measure, never click on any link in an email. Especially to logon to an account.
The safest thing to do, is to go to your Internet browser and manually type in the website name such as www.yahoo.com logging in from there.
The way that the fake email links work is they take you to a dummy login page, where you will enter your username and password. In the background your details are recorded and the Web browser is then redirected to the proper Yahoo login where you will be logged into your account so that all appears normal. The fraudsters now have a copy of your username and password to do with as they will.
If you believe that your account has been compromised, such as it is sending out spam, then the first thing to do is change your password.
Make your new password a more secure 16 digit one. If you are still having issues, we have solutions.