We recently became aware of an ongoing security risk related to Apple ID accounts. As a result, we strongly recommend that you immediately change your Apple ID password (if you have one). We also recommend that you enable two-factor authentication for your Apple account.
To change your Apple ID password, please follow these instructions: http://www.wikihow.com/Change-Your-Apple-ID-Password
To enable two-factor authentication for your Apple account, please follow these instructions: http://www.wikihow.com/Turn-on-Two-Factor-Authentication-on-an-iPhone
The finer details:
Recently a hacking group has claimed that they have obtained hundreds of millions of Apple account usernames and passwords. They are currently attempting to blackmail Apple for at least $100,000 before they start remotely wiping millions of Apple devices. Apple denies that their servers have been compromised and this threat is looking more and more false.
You can read an article regarding this situation here: http://www.theverge.com/2017/3/28/15092076/apple-icloud-hacking-threats-turkish-crime-family-credential-stuffing