Since you can get to yahoo mail anbd login with your normal ID, but get the msg when you try an old ID
I suspect yahoo is looking up that id and presents an old server with an out of date certificate on a secure connection (HTTP
S) --> SSL is protecting you.
Best advice when you get that message is to close the window.
That being said, it doesn't hurt to scan your machine for malware.
What Antivirus do you have?
Have you run a full scan (including PUP, PUM)? Possibly a scan is scheduled.
Download, install, and run a FULL scan with
Malwarebytes' (Mbam)
:warn: When installing Malwarebytes,
do NOT elect the free trial of the full version; you want the free version.
:warn: Watch out for extras (Toolbars, Search providers, etc) that might be packaged with the installer
UNTICK anything that is not Malwarebytes.