Governments do it, companies do it, criminals do it. But in recent years some of the highest profile computer hacks have come from so-called hacktivist groups. Each week hackers target a new organisation or government website. Many of these hacker activists claim to belong to the amorphous group known as Anonymous or an off-shoot of it. Their aim? To wrest control of the internet from states and big corporations and give it back to the people. Or simply to have fun.

The FBI, the Metropolitan police, the US Senate, Sony, PayPal and Visa have been some of the highest profile victims of the hackers. More often than not the attacks come in the form of DOS, or denial of service, attacks - effectively flooding websites with requests so that they crash. In some cases the hackers have managed to steal personal and financial records from the organisations and then post them online. Sometimes the reason given by the hackers for these attacks is as a response to official actions taken against Wikileaks or attempts by the authorities to close down certain websites, such as free music download sites.

The FBI and police have had some success in tracking down some of the hackers - many of them just teenagers.

In "The Hackers" Simon Cox delves into the strange world of hacktivism, as he tracks down some of these hackers and speaks to those trying to catch them.

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