Per prevenire furti di credenziali Apple dice ai suoi utenti di controllare il certificato del sito di iCloud

Apple is deeply committed to protecting our customers’ privacy and security. We’re aware of intermittent organized network attacks using insecure certificates to obtain user information, and we take this very seriously. These attacks don't compromise iCloud servers, and they don't impact iCloud sign in on iOS devices or Macs running OS X Yosemite using the Safari browser.

The iCloud website is protected with a digital certificate. If users get an invalid certificate warning in their browser while visiting www.icloud.com, they should pay attention to the warning and not proceed. Users should never enter their Apple ID or password into a website that presents a certificate warning. To verify that they are connected to the authentic iCloud website, users can check the contents of the digital certificate as shown below for Safari, Chrome, and Firefox—each of which provides both certificate information and warnings.

via support.apple.com