I have always felt reluctant to get involved in a conversation about nude photos of Jennifer Lawrence or Scarlett Johansson. Always. Even before I knew there were any. When someone hacks your iCloud account, it is a breach of privacy issue, clearly. It is a feminist issue, of course.

But it is also a cultural issue, about naked selfies. Even to ask that question, "who takes naked photos of themselves?" makes it sound, at the very least as if you don't take the breach of privacy seriously, and at worst, as if you're blaming the victim for the invasion. And yet … when you don't ask, "who does that? Who has naked photos in the cloud in the first place?", then you don't find out. Which is a big hole in your knowledge, because the answer is everybody. Everybody but you.

"Technology's my thing, it's how I made my living for many years," said Matt, 42. "I specialised in high-speed digital comms, the backbone of the internet and how your phone talks to it. Then we went to 3G, so we could shift data. And that's when it all changed. Your phone is not a phone any more, it's just a data terminal. You could talk to your friends, or you could equally snapchat them. You might send an image with text on it …"

OK. And then how do you come to be naked?

"I'm a semi-single parent, I don't tend to have a long-term partner, I'm either working or I'm travelling or I'm doing childcare. So I'll have a partner for six months, I'm serially monogamous. If I'm away, I'll send them an image, they'll send me an image. You don't just do it without talking about it; that's like groping a stranger on a train. You raise it. If they say 'that'd be a laugh', then I'll say – only use your phone, make sure that you've got Cloud storage turned off. I'll usually tweak their phone so that it's right. After that, we're in control of it, so it's a trust issue between me and them."

It's not a young thing; but it does seem to be young people who've adopted the image-as-conversation.

Julia, a 22-year-old English student, said: "I can only think of two people my age who haven't done it. It becomes like a sort of weird correspondence. If I snapchat someone a pic, they would send one back." This is just a regular part of dating. "It's sort of like a flirty thing, you meet a boy on a night out, you'd snapchat him a picture instead of texting him,"

But you've only just met him … a picture of what? "Probably like top half, there's a lot of bra and knicker shots." Snapchat self-destructs in a given number of seconds, and if they try to screengrab it, you get a notification. "But it's never happened where somebody's screen-shot a nude. It's one of the unspoken rules, you just don't do it."

The classic way for a photo never to come back to haunt you is to cut your head out of it. Ben, 22, said all his female friends did this. He, on the other hand, "will send naked photos to a boyfriend, but I will generally do comedy ones. Just, like, normal photos, but you'd have your penis hanging out. They were not sexy at all. It was just, like, 'hi'."

The joke element runs strong in the naked selfie. Caroline, 26, who I interviewed last year, said: "My friend takes pictures of herself from weird angles, as a joke, then sends them to her friends saying 'tits or arse?'" But it's mainly a sex thing. It's not an irony-that-happens-to-be-naked thing.

Imogen, 37, had naked photos of herself hacked from Instagram. "With even basic technical knowledge, it's amazing how easy it is to hack into people's accounts. For me, the thing with selfies, I don't really care. I'm not that fussed about nudity. Being able to know that it is private is more important to me than whether or not someone has seen my arse. I don't hate my body.

"But people can be vicious. Expressing yourself on social media connects you unwittingly to a much larger and much darker … I don't even know what it's called."

Yet that side of it is more of a conundrum – how to keep this stuff private – than a deterrent. Because at its core, it has nothing to do with the peeping Tom. It's about people sending photos to one another; citizen porn, if you like.

Ben concluded, "I can't imagine a relationship where someone said, 'I really want you to send these photos and why won't you?' It's not that at all. It either happens or it doesn't."

• All names have been changed