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| Anonymous is known as a hacktivist group, pursuing its agenda through online attacks. |
Hacktivist group Anonymous has briefly taken offline 40 sites it claims traded in images of child sexual abuse.
As part of the action it published the names of 1,500 people who it says used a site known as "Lolita City".
The attacks were carried out as part of Operation Darknet which targeted abuse groups that swapped images via the Tor network.
Experts condemned the attacks saying they could have scuppered ongoing investigations or tainted evidence.
Vigilante action
The Tor network tries to aid anonymity by routing web browsing queries through a series of servers scattered around the net. This makes it harder to trace users and monitor what they are seeing.
Many protestors, in nations such as Egypt and Syria, use Tor to hide their location from authorities.
One innovation, recently added to Tor, is the ability to create a "darknet" - a network that works in a similar way to the web but can be seen only by Tor users.
In early October, Anonymous hackers noticed that one site hosted on this Tor darknet contained links to images of child sex abuse.
Anonymous members removed the links but they were soon re-posted. It knocked the site offline with a denial of service attack and worked out which firm was hosting the links.