There are many news reports of Celebrities getting their accounts hacked and then pictures were taken in their archives of a compromising nature.
It is evident that everyone needs to have Two Factor Authentication (2FA), where it does not take just a password to enter the account. On a new computer the first time access must be granted with a password and an additional device, like a code to a cellphone.
Here is Apple's tech support information for iCloud 2FA:
Simple, once you know of it.
Of course also having a password that is long would be also good, I doubt the actors and actresses have 14 digit passwords with numbers and capital letters.