Apple has just released a press statement updating its investigation into the weekend breach of celebrity photos. As noted in the press release, the company says that none of the cases investigated were the result of any breach of Apple's systems including iCloud and Find my iPhone. Apple believes that it was a "very targeted attack on user names, passwords and security questions" that caused the breach -- essentially saying that it's most likely a social engineering attack that made the photos vulnerable to being exposed to the public.
Apple reiterates that using a strong password and two-step verification can help protect against this type of attack.
Update to Celebrity Photo Investigation
We wanted to provide an update to our investigation into the theft of photos of certain celebrities. When we learned of the theft, we were outraged and immediately mobilized Apple's engineers to discover the source. Our customers' privacy and security are of utmost importance to us. After more than 40 hours of investigation, we have discovered that certain celebrity accounts were compromised by a very targeted attack on user names, passwords and security questions, a practice that has become all too common on the Internet. None of the cases we have investigated has resulted from any breach in any of Apple's systems including iCloud® or Find my iPhone. We are continuing to work with law enforcement to help identify the criminals involved.
To protect against this type of attack, we advise all users to always use a strong password and enable two-step verification. Both of these are addressed on our website at http://support.apple.com/kb/ht4232.