About four in 10 women say they’ve received photographs from men that they certainly didn’t ask for—the dreaded image colloquially known as a “d-ck pic.”

Sometimes these unsolicited penile pictures invade an unsuspecting woman’s phone via AirDrop — a function on iPhones that allows one user to share files with others nearby — while she sits, unassumingly, on the subway, at a restaurant or at the movies. The anonymous attacks have apparently become so widespread in the U.K. that some in the British government are calling for a law targeting these “cyberflashers.”

These forced phallic pics have, until recently, been treated as a just a joke by those who haven’t received one.

“The research in this area is really limited,” Laura Thompson, a University of London researcher whose work focuses on harassment over dating apps, told The Guardian. “I think this blind spot says something about how society and the law tends to think of the problem: that d-ck pics are an annoying internet phenomenon as opposed to ‘real’ flashing. Research reflects the world we live in, and I just don’t think this problem has been taken seriously until relatively recently.”

But why do men — of whom, only 5% admitted to ever sending a shot of their modeled member — feel the need to send such explicit images to women?

The answer, of course, is as varied as the pictures themselves.

“There’s always a tendency with these issues to provide one kind of formulation; a one-size-fits-all explanation,” said clinical psychologist and psychoanalyst, Stephen Blumenthal. “But the reality is that there are many different motives that people have, some of which are perhaps more troubled and troubling than others.”