Apple has recently acknowledged to Forbes the existence of a security issue in iTunes that allows such "relatively easy" to find out the access data of users and thus access backups of them.
Apparently, due to changes in the protocol for verifying passwords, now the data is more accessible by brute force, ie try a large number of passwords until you find the right one .
In any case, that this security flaw becomes a real problem you require that the perpetrator have physical access to data in the computer that has been done the backup, so in this sense we remain quiet.
Thus, the backups are performed using iCloud is not affected, but how I said, no one should worry about the privacy of your data even if you made the copy through iTunes.
Still, personally I recommend using passwords containing alphanumeric characters with uppercase and lowercase letters in between, making it difficult, and much, that the perpetrator can successfully perform the attack.