Here's the letter (note that I changed the links to images so they are not active links):
Due to congestion in all Yahoo! Mail user accounts, there shall be a removal exercise of all used and unused Yahoo! Accounts. Yahoo! Inc would be shutting down several accounts.
You will have to confirm your Yahoo! account. So you are required to logon to your Online Yahoo! Account with the provided link below.
NB: Failure to to update your Yahoo! account will result to a permanent closure.
Thank you for being a loyal Yahoo! Mail user.
We hope you enjoy the newest version of Yahoo! Mail.
Yahoo! Mail Product Management
Looks legitimate, right? Well, if you put your mouse on top of that link, your browser will tell you where the link actually goes. On most browsers, the actual link destination will appear on the lower-left corner of your browser window when you put your mouse on top of the link. In this case here is the actual destination address behind this seemingly valid link:
Now if you were to actually click on the link and go to that website, here is the page you will get to:
You'll see that they took enough effort to really try and make it look like the Yahoo mail site but if you look closely and take a look at the browser address bar (at the top of your browser page), it will show that you are not on the Yahoo page at all.
So next time you get a notice from your email provider, or your credit card company, or your bank, or any other online place you have accounts with, be extra careful that you're not falling into a trap.