The Australian research also revealed that overwhelmingly male, well-educated, and aged anywhere from 18 to 80 indulge in such kind of 'pleasure'.
They spend an average of just over 12 hours on the sites each week - mostly chatting, participating in cyber sex with webcams, downloading video and images, or sending erotic emails, the study found.
The research revealed that more than 65 per cent of the 1325 American and Australian men surveyed said they had met someone off line that they had first encountered online.
Marcus Squirrell, a doctoral student at Swinburne University of Technology in Melbourne, said the study, to be presented at a major psychology conference tomorrow, was the first to paint a full picture of cyber sex surfers.
Most concerning was the high rate of poor mental health among the sample group.
"We found that 27 per cent of them were moderate to severely depressed on the standard depression scales," Sydney Morning Herald quoted Squirrell, as saying.
"Thirty per cent had high levels of anxiety and 35 per cent were moderately to severely stressed, which is of course extremely high," Squirrell added.
The more heavily they engaged in online sexual activity the higher their level of depression and anxiety was, he said.