[Useless]

http://news.bbc.co.uk/2/hi/technology/10289009.stm

Many others used "shady" practices to keep visitors onsite. These included javascript catchers that made it hard for people to leave a page.

Others use scripts that re-direct visitors so when they click on a link they do not see the video or image they were expecting but are passed to an affiliate site.

The vast majority of sites engage in this trading of traffic or clicks, said Dr Wondracek.

"Visitors are being abused as click bots," he said.

As most sites were free, the only resource they could exploit as a revenue source was this traffic.

"It's cut-throat competition," said Dr Wondracek. "Everybody tries to get as much traffic as possible."