Yesterday, a group calling itself the Iranian Cyber Army hacked Baidu.com (China's most popular search engine), shutting it down for three and a half hours. It is unclear what the reason behind the attack was or why Baidu was the target. The attack was on the domain name server that operates in the US (though I'm not sure why Baidu uses US servers).
China has been an ally of Iran--blocking most actions by the UN against Iran in recent years. However, China has also been silent on the political unrest in the country.