As you know, I have been on the internet since 1983. That means I come from the era of ARPANET, teletype terminals, text-only browsers, UUCP, Usenet, 100 baud modems, and NSFNET.
The most important thing I learnt about the internet in this era is that it was built initially by very few things: The Department of Defense of the United States' Military establishment, the US DoD scientific and engineering researchers, the US DoD civilian contractors, and US University researchers. This was followed up by the Government communication, academia in general, Corporate America, and European followed by world-wide scientific concerns. In 1990, the US DoD handed control of the internet backbone in the United States to the National Science Foundation.
Note that what we use is largely built by the US and its military allies. In my era, it was tacitly assumed that the DoD could read all our communications if it really wanted to. Most of us used to joke that they still monitored everything even after "handing control" over to the NSF. (They couldn't have because the connections were too slow and the processing speeds were small, but we always knew it was theoretically possible.) Because the main internet nodes still contain the old backbone, I always assume that the DoD can read everything I put out there. That's why the whole Eric Snowden flap didn't faze me at all - I already assumed they were collecting information.
The growth of the internet in the 1990's was largely by geeks like me who didn't have GFs, liked Science Fiction, had social lives that revolved around our limited interests and worked at governmental institutions that had internet access. We were almost exclusively male. Hence, the early internet was built up due to an interest in SF, science, technology, and the sex we weren't getting because women turned up their noses at us.
Which brings us to "the fappening." Why are the pictures almost always of females? Because those who grew up in this culture are largely male (Def-Con attendees put this at a maximum of 15% - where most are often off-put by their treatment by the males) who often need an escape from bad social lives, among other things, they are often interested in young women. The psychology of many of these people are the same as the revenge porn posters you know about, except they target female celebrities instead of females they know.
Because of the complexity of the code required to run your local device(s) and the hardware infrastructure of your ISP and data providers, you can expect breaches like this to happen every now and then. Even if the code to a security system is well-vetted, it is still possible that there is a flaw - and even if it is found, it is entirely possible that something gets lost in the shuffle. There are also limitations within the hardware, within the embedded software, and the like that can be beaten no matter how good the code is. So anything that you use an electronic device to send, receive, save, delete, etc. probably exists somewhere and can be had by anyone who tries hard enough.
Moreover, even if you delete something from any computer system, odds are that it is not deleted. Usually, all that is done is that the location that stored the location of the file in memory is deleted. However, until some part of that memory is used again, that file will exist indefinitely. Thus, even if your file is "deleted", a good hacker who knows what he's doing can get at it. Moreover, companies who allow you to save photos probably upload any picture from your device to their cloud so that it can be reloaded if your device fails. So that's two places - one that you probably don't have direct access to - from which you would have to delete a file PROPERLY in order to remove evidence of its existence. And that doesn't even count back-up tapes or whatever that the company may have.
Oh, yeah - and any intermediate machine used in transporting your data may have it available as well. Now, those intermediate copies will eventually be getting blown out because of the high traffic that goes through them, but probably for a bit, they are available. And that doesn't even count any logging that someone along the way may be doing.
So no matter what I do online, like write a blog something on an iCarly fan page, everything is literally available forever for anyone who tries to find me. And they can figure out where I posted this from if they really wanted to. Check out the books in the security section from No Starch Press.