Police have arrested a 41-year-old man in connection with a cyber attack on websites connected to home secretary Theresa May.
He was arrested in Stoke-on-Trent for questioning under the Serious Crime Act on suspicion of assisting or encouraging crime.
Metropolitan Police said the suspect allegedly encouraged distributed denial of service (DDoS) attacks on both Theresa May's constituency website and the Home Office website in June.
The suspect was released on bail pending further enquiries as specialist officers examine computers and other digital equipment seized during the arrest, the police said.
DDoS attacks, which make websites inaccessible by flooding them with access requests using botnets of computers distributed over a wide area, are increasingly been used by blackmailers and protesters.
Supporters of the technique claim it is a legitimate form of protest, but taking part in or encouraging such an attack carries a jail sentence of up to 10 years in the UK, police warned.
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A police spokeswoman declined to comment on whether the man arrested in Stoke-on-Trent was an Anonymous supporter or member of any other activist group, according to the Telegraph.
In April, a study revealed financial services firms were targeted by three times as many DDoS attacks in the first quarter of 2012 than in the previous three months.
In July, Chinese and Hong Kong police arrested blackmailers threatening commodities and securities traders with DDoS attacks.
One of the most recent attacks on the financial sector was in October, when HSBC said servers had come under a DDoS attack which affected HSBC websites around the world.