Hacker group Anonymous has claimed to have defaced around 500 websites in China to protest against the Chinese government's strict control of its citizens, BBC reported.
The targets included government sites, official agencies and trade groups among others.
The websites defaced had a same message posted on them that chided the government for its repressive policies.
"Dear Chinese government, you are not infallible, today websites are hacked, tomorrow it will be your vile regime that will fall," it read.
The group urged Chinese people to join Anonymous and stage their own protests against the government.
The announcement about the defacements was made via an Anonymous China account.
A list of the 485 sites affected was put on another website called Pastebin, said BBC.
Separate Pastebin messages showed email addresses and other personal details that were stolen when sites were penetrated.
China has one of the most comprehensive web surveillance systems in the world, dubbed the "Great Firewall of China".
The BBC said the system "reinforces its broader social controls. The system polices where Chinese people can go online and tries to restrict what they can talk about".
On the defaced pages, the Anonymous attackers also posted links to advice that could help people avoid official scrutiny of what they do and say online.
There has been no official confirmation of the defacements. Media reports said government officials denied any hacking had taken place.