Were you signing into an iPad about the time you received the message? If not, are you sure the message is legitimate? Does it contain a link for you to sign in somewhere? It may be a scam. Consider changing your password as a precaution.
Apple will always address you by your name or the name they have on file for you, not Dear Customer, Dear Client or by using your e-mail address. The e-mail will be from @apple.com or @iTunes.com. E-mail addresses can be spoofed. You can go to Mail/View/Message/Show all Headers to see more. Apple e-mails will never contain an attachment. Apple will never request personal information such as Social Security numbers.
Avoid phishing emails, fake ‘virus‘ alerts, phony support calls, and other scams
Send the e-mail to Apple as an attachment to a new e-mail before deleting it. You can forward as an attachment by going to Mail/Message/Forward as attachment.
Apple ID Password Change
What to do after you change your Apple ID or password - Apple Support I suggest doing this before you change your Apple ID or password.