The email address that it was sent from is
security-update@amazon.com. Here's what it says:
Hello,
At Amazon we take your security and privacy very seriously. As part of our routine monitoring, we discovered a list of email address and password sets posted online. While the list was not Amazon-related, we know that many customers reuse their passwords on several websites. We believe your email address and password set was on that list. For your security, we have assigned a temporary password to your account.
You will need to reset your password when you return to the Amazon.com site. To reset your password, click "Your Account" at the top of any page on Amazon.com. On the Sign In page, click the "Forgot your password?" link to reach the Amazon.com Password Assistance page. After you enter your email or mobile phone number, you will receive an email containing a personalized link. Click the link from the email and follow the directions provided.
Your new password will be effective immediately. We recommend that you choose a password that you have never used with any website.
Sincerely,
Amazon.com
http://www.amazon.com