The online call coincided with demonstrations across the world this past Sunday, which also called for the artist's release. Ai, who is also known for his activism, has been detained as part of a Chinese on political dissidents in the country.

Authorities in the country have arrested other human rights activists and clamped down on the information flow, following previous online postings that began in February calling for a "" against the Chinese government.

Change.org is currently blocked in China. Internet censors in the country regularly block sites that are deemed to politically sensitive.

Despite the block, the computers involved in the DDoS attack are managing to find a way around the country's national Internet firewall, said Rattray.

In the past, other sites have been the victims of cyber attacks coming from China. This March, blog publishing platform WordPress.com also originating from China.