Image caption Tor makes data hop across lots of different nodes to hide where traffic is going

Austrian police have seized servers that were part of a global anonymous browsing system, after images showing child sex abuse were found passing through them.

Many people use the Tor network to conceal their browsing activity.

Police raided the home of William Weber, who ran the servers, and charged him with distributing illegal images.

Mr Weber denied the charges and said he had no knowledge of what people did via the servers, which supported Tor.

'Anything goes'

The Onion Router (Tor) was invented by the US military as a way to conceal official use of the net. It pipes data through many different nodes, like the layers of an onion, to hide who is browsing what site.

Mr Weber operated part of the Tor network known as an "exit node". These powerful servers act as a link between the wider net and the cloud of computers forming the core of the Tor network.

In total, Mr Weber had operated seven Tor exit nodes that had piped terabytes of data every day between the two networks, he revealed in an interview conducted after the raid.

"I mainly run the exit nodes to make it possible for the not-so-privileged folks to have uncensored access to the internet, without fear of government prosecution," he said.

The police raided Mr Weber's flat and took away the 20 computers he had there. However, he said, the server police had said had been used to distributed the illegal images was in Poland and was currently offline following complaints from Polish police about it being used in hack attacks.

After the raid Mr Weber was interviewed by police who, he said, had become "more friendly" after he had explained how Tor worked and that he was not responsible for what people did via the anonymising system and had kept no "logfiles" of activity.

Mikko Hypponen, chief research officer at security firm F-Secure, said although Tor had many laudable uses, others were content to abuse it.

"It reminds me of the web in 1995," he said. "In those early days, once people got the hang of it, anything goes as there seemed to be no law, no police and no regulation."

"People trust they will never be found when they are on Tor," he said.

Mr Weber is appealing for donations to help fund his legal defence and establish a legal precedent to help protect other operators of Tor exit nodes from similar police attention.

He potentially faces a lengthy prison sentence if found guilty of distributing images of child sex abuse.