Sounds like a scam to me..

If you click on the link, you will download a virus onto your computer/phone/tablet, etc. I received it as well, but the address it was sent from did not match Yahoo's e-mail accounts. When Yahoo upgrades their mail, it is usually on the page where your inbox is, and will ask if you want to upgrade to the new mail, or continue to use the "classic" mail...they don't send e-mails.  

Oh, and I only received this e-mail in my provider Yahoo....my personal Yahoo did not receive this e-mail..hence, it is someone getting e-mails addresses from one of these boards.  

Yup, got a Lockdown Email but I ignored it. There was another one that went out but the other email that went out actually had a misspelling which was a dead giveaway to it being a fake. And how is Yahoo going to lock me out of my email if I don't "upgrade". Um, it's up to me and my computer or android as to what version I use and want to have installed. These hackers are creative just not creative enough in my book!