Just under a third of teenagers have experienced some form of online harassment or 'cyber-bullying', according to a US study.

The most common form of harassment was having a private communication forwarded, followed by being the victim of an online rumour, or being sent aggressive messages, the study concluded.

About one in six teenagers had experienced having a communication they thought was private - such as an e-mail or text message - forwarded on to others by the recipient, and a slightly smaller percentage had been threatened online, the report, by the Pew Internet & American Life Project, said.

Overall teenage girls were more likely to be have experienced cyber-bullying than boys - 38 per cent of girls reported having been victims, as compared with 26 per cent of boys - with the number rising to 41 per cent among girls aged 15-17, the most affected group.

Teens who used social networks were also more susceptible - 39 per cent of those who were on networks such as Facebook and MySpace had been bullied, as opposed to 22 per cent of those who were not.

Fewer than one in 10 - 6 per cent - reported having had an embarrassing photo of themselves posted online without their permission, however.

"Bullying has entered the digital age," the report's author, Amanda Lenhart, said. "In the past, the materials of bullying would have been whispered, shouted or passed around. Now, with a few clicks, a photo, video or a conversation can be shared with hundreds via e-mail or millions through a website, online profile or blog posting."

The report surveyed 935 US teenagers aged 12-17.

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