Apple implemented two-factor authentication for its iCloud service earlier this week, effectively following through on its promise to up its security measures after the theft of high-profile celebrity nude photos over Labor Day weekend.

If a user opts in to the new authentication system, they will have to supply a mobile device number, which will then receive a verification code text whenever an attempt is made to log into an iCloud account, according to the company’s FAQ page. A verification code will also be needed to manage a user’s Apple ID at My Apple ID or to make an iTunes, iBooks or App Store purchase from a new device.

Apple will also provide a recovery key for users who lose access to their mobile device.