Apple has added a new layer of security to iCloud, notifying users when someone logs into iCloud.com using their email address and password. When you log in to the site, Apple will send you an email notifying you that someone has your credentials have been used on iCloud.com, and instructing you either to ignore the email if you did this yourself, or what steps to take if you didn't.
Full story from the iMore Blog...
Facebook
Twitter
Instagram