Most people use their Apple ID account not only for iCloud data, but to purchase content from iTunes and the App Store. That means that anyone who gets ahold of your account or manages to change your password could have access to your personal information and credit card information. If you want to increase the security of your Apple ID, you can use two-step verification to add a second layer of protection. That, it requires something you know (your password) and something you have (the security token sent to you) to access your account information and make changes.
What does two-step verification protect?
Currently two-step verification is required for the following activities:
Sign in to My Apple ID to manage your account
Make an iTunes, App Store, or iBooks Store purchase from a new device
Apple has tested two-step verification on other parts of the iCloud service, and hopefully they'll roll it out across all services quickly and completely in the near future.
What if I have multiple Apple ID's?
If you have multiple Apple IDs, for example, if you have a separate iCloud login from your iTunes login, you can still set up two-step verification for both. You can do this by verifying an SMS-only device on the second ID. As always, you can use your recovery key if it is every unavailable or simply fails.
How to secure your iCloud account with two-step verification
In order to enable two-step verification, you must have a current password that meets Apple's minimum standards of 8 characters complete with at least 1 number and 1 capital letter. If you have to change your current password in order to meet this standard, you'll have a short waiting period before you can enable two-step verification.
Go to appleid.apple.com from the browser on your Mac or PC.
Sign in to the Apple ID you'd like to enable two-step verification for.
Click on Password & Security in the left hand navigation.
Answer the secret questions you've previously set up and click on Continue — if you don't remember them, you can reset them if you have a backup email on file.
Click on Get Started... under the Two-Step Verification section.
As long as you have a device linked to your iCloud account on hand, click Continue on the next screen.
Read the next two screens about two-step verification.
Once you understand what they're describing, click Get Started on the second screen.
Add your current phone number to start the verification process.
Check your phone for a text message and then enter the 4-digit verification code.
After your phone number is verified, a list of connected devices you can verify should appear.
Click on Verify next to the devices you'd like to trust in case you need to use them for two-step verification in the future.
Once you're done verifying all your devices, click Continue.
The next page gives you your Recovery Key which you'll need to either print out or write down. Do that now.
Once you've gotten the code written down or printed, click Continue and then verify it by typing it out on the next screen. You won't be able to continue until you confirm you know the code.
Click Confirm in order to continue.
Click the checkbox to confirm you understand what you'll need in order to complete two-step verification should you forget your password.
Click Enable two-step Verification.
You'll receive a confirmation that two-step verification has been enabled. Click Done.
That's it! Two-step verification will now replace security questions. Remember that in order to regain access to your iCloud account, you'll need any TWO of the following:
Your Apple ID password
A trusted device
Your recovery key
If you don't have two of the listed above, you'd need to create a new Apple ID.
Note: Originally published, March 2013. Updated, February 2015.