Teenage boys are using Facebook to shock girls by uploading hardcore pornography to the social sharing site.
A survey by the University of East London found 66 per cent of girls aged between 12 and 16 had seen pornographic content – all of them via Facebook.
Amanda Roberts, a psychology lecturer at the university who created the study, told the Telegraph: "It is shocking content; it seems the boys are putting it on there to shock them.
"It's like back in the 1950s where boys would run around girls with worms. It's just different ways now.
"They are friends with so many people they can't block it; it comes through on their phones. We're talking about quite hardcore things."
The explicit images provoked emotions of fear, confusion and anger in the girls, and they felt worse the more they watched.
Almost all of the boys had seen porn, but they mainly felt excitement or happiness when viewing it.
Of the 14-year-olds who had seen porn, 29 per cent of boys said they spent 'a lot of time' watching it, while none of the girls regularly watched it.
Ms Roberts said: "Initially the girls were seeing it for shock value with friends. When they got older, a little proportion started using it for sexual purposes."
She described the porn viewed by the girls as 'hardcore' and 'shocking' and said one of the most popular videos shared on Facebook was a man inserting a glass bottle into his anus.
Other types of porn viewed included 'murder porn', 'Harry Potter porn', 'Japanese anime hentai porn' and 'slash porn', which depicts sex scenes between two 'celebrities'.
Ms Roberts said: "I think schools should talk about porn. I don't think we will be able to stop it because it's out there, but if you can educate them and say that's not how it is all the time, then it would help people be less frightened by it."
The research will be shown on a Channel 4 documentary Porn on the Brain tonight at 10pm, as part of Channel 4's Campaign for Real Sex.