Apple has sent out a support email explaining that, starting June 15, third-party apps using iCloud to store data will require app-specific passwords across the board. If you want to continue using your favorite third-party app with your iCloud account, you'll have to enable two-factor authentication and generate individual passwords for each app.
The email was reported on originally by MacRumors.
Beginning on 15 June, app-specific passwords will be required to access your iCloud data using third-party apps such as Microsoft Outlook, Mozilla Thunderbird, or other mail, contacts and calendar services not provided by Apple.If you are already signed in to a third-party app using your primary Apple ID password, you will be signed out automatically when this change takes effect. You will need to generate an app-specific password and sign in again.
I know this sounds like a serious inconvenience, but in light of how many malware attacks have been taking place around the world, and with such severity, app-specific passwords will ensure your private data is locked down with a deadbolt and protected with a body guard. In other words, it's worth it.
With two-factor authentication set up no one can access your Apple account without you knowing about it, even if someone has your password. You'll get a notification on a trusted device requesting your confirmation that you're the one trying to access your data.
With app-specific passwords required for third-party apps, you'll be able to allow your favorite apps to link to iCloud without having to enter your Apple ID password, potentially exposing you to attack.
If you don't already have two-factor authentication enabled, you'll need to do so if you want to continue using apps that access iCloud.
How to enable 2-factor authentication
Once you have two-factor authentication set up, you'll be able to generate app-specific passwords from Appleid.apple.com.
