I made a Yahoo email account a long time ago when I thought I was going to have to change my email provider when I changed satellite internet companies. I was able to keep my old account and have never used the Yahoo account. Recently Yahoo suddenly began sending an intrusive invitation to use their services (see image). It pops up on my desktop and can’t be minimized, moved, or deleted. I found out that it was somehow using Thunderbird to get to my computer. When I hovered over the Thunderbird icon on my taskbar both Thunderbird, and the Yahoo ad displayed, and when I closed Thunderbird, it didn’t pop up. I went to Yahoo and closed out my account. No joy. How do I prevent this malicious advertisement from using Thunderbird?