There is no doubt that Apple’s iCloud service is a complete package. It brings everything email, calendar, contacts, “Find My iPhone” and cloud storage under one roof. It is also true that any one can access that with single username and password. 

“It all sound very perfect and convenient but the picture is not complete yet, there is more to it. Imagine that single username and password is hacked then one can lose literally everything” reported by UK based news website TheNewsTribe.

Same happened with Mat Honan, former journalist for Gizmodo and former contributing editor to WIRED magazine. Hackers got access to his iCloud account first before messing up with his Twitter account. His password contained seven characters and was alphanumeric.

There is also reported that “Gizmodo reporter is hacked via Apple tech support”.

And all this damage was done just because of single username and password. According to Honan, his password was gained by brute forcing i.e. trying various passwords until you get lucky.
“Short passwords are very dangerous as they give a false sense of security,” Mat Honan said after being hacked.
One of the major drawbacks of iCloud is that everything can be accessed through single account while Google provide a two step verification, which requires a code every time you log in and Google send that code on your phone. The process is a bit irritating but it improves the security a lot.
So it is better to think of something if you own an iCloud account or go for an alternative before someone mess with your account.