As an experiment I fired up a Chrome browser and logged into my own email account with BT.
As soon as I typed in my password (concealed by asterisks) a number of asterisks (stars) became added on to the end of my password, but pleased to say that it all worked OK and there was no problem in sending or receiving emails
I do know that BT have changed their email system fairly recently, so it may be as a result of the changes.
I know that the machine I used to access my BT email was clean (no virus or malicious code) so I am relaxed about the situation on my machine.
If you think however that your machine may be infected then you could drop in on our Virus and Spyware Removal forum, post the required logs and have your machine checked for malicious code.
If you do this, then please enclose in your post to them a link to your topic here, so that the malware team know what has been going on.
Here's a link to the Virus and Spyware removal forum.