Change.org, an online petitioning platform, is the latest victim of an organized distributed denial of service (DDoS) attack allegedly originating from China, believed to be caused by the site’s call to release artist Ai Weiwei from custody.

Under the DDoS tactic, malicious codes infect computers to trigger mass attacks against targeted websites. The attacks, which started late Sunday, have nearly brought down the site. According to Change.org founder Ben Rattray, ”the current attack originates from an expanding group of computers primarily based in China, and has yet to stop.”

Change.org was attacked after it has hosted an online petition calling for the release of Chinese artist Ai Weiwei, a popular Chinese activist detained by the Chinese government. The petition is one of Change.org’s most successful international campaigns, attracting almost 100,000 people from 175 countries.

“It’s pretty clear the attack is in response to the campaign,” Rattray said. Despite Change.org being blocked in China, Rattray speculates that the computers involved in the DDoS attack are managing to find a way to circumvent the country’s national Internet firewall.

There’s really no way to be certain where the attacks originate from because there’s also the possibility that the computers are under the control of hackers based in another country.