Hacker collective Anonymous has hacked 30 Chinese local government websites to protest the arrest of five hacktivists in October 2014, who are accused of sending additional traffic to a Hong Kong government website during the pro-democracy protests.

The Hong Kong protests started in September 2014, bringing the city to a standstill, and although the former British colony is now back on its feet, protests against rule being imposed by the central government in mainland China remain.

What is a DDoS attack? DoS (Denial of Service) attacks are malicious attempts to disrupt a network service or website by targeting its servers with rapidly repeated requests for connection. This overloads the server's resources and effectively blocks legitimate users from connecting to it. DDoS (Distributed DoS) attacks are an evolution of this premise, whereby multiple systems contribute to flooding a server. This is often done using botnets and/or software operated by users intending a coordinated attack.

Anonymous claims that it chose to launch "Operation China" - a campaign of Distributed Denial of Service (DDoS) attacks against Chinese government websites - on 10 April due to the recent arrest of Hong Kong hacktivists due to their alleged involvement in cyberattacks against Chinese websites during the protests.

"Some hacktivists have been arrested and persecuted by the Chinese Government. Five activists have been arrested accused of causing congestion in [sic] Chinese sites, and this kind of protest is one of the most peaceful imaginable," Anonymous wrote on Pastebin.

"Pro groups China attacked the protesters, firing at them. Demonstrators were beaten and sexually harassed, but no one helped, the streets were stained with blood. The police remained inert and ignored these aggressions, and started arresting people who were being attacked. This makes us believe that the attackers were, well, paid the government or pro-China parliamentarians."

As of 9am BST on 13 April, the 30 websites Anonymous claims to have attacked are still offline. The hacked domains include the local government websites for many cities in China, including Huazhou and Fengshun County in Guangdong, Wulian County in Shangdong and Cili County in Hunan.

A sub-domain for the Hunan news website belonging to China's state-owned telecoms company China Telecom is also down.

The hackers also brought down the Hunan Police Academy website over the weekend, but it is now up and running again.

The Chinese government maintains strict laws where any kind of dissent, both online and offline, is concerned.

On 2 April, three Chinese citizens were arrested in Guangdong province on suspicion of "incitement to subvert state power", for posting tweets featuring satirical and pro-democracy content, as well as critical comments about President Xi Jinping to social media, including Tencent's QQ instant messaging software.