Watson Meng, who runs the Chinese-language Boxun site from Durham, N.C., said he believes an element of the Chinese government ordered the attack, which disrupted access to readers much of Thursday, but has no proof, The Washington Post reported.
Boxun has been targeted in the past while publishing material the Chinese government deemed sensitive.
Of the attack, Meng said, "It's obvious that it's related to what we have been reporting recently."
Chinese Internet users access the site through proxy servers that circumvent China's Internet firewall, which the government relies on to block some content.
Chinese Embassy spokesman Geng Shuang denied the government had anything to do with the disruption.
"The Chinese government prohibits online criminal offenses of all forms, including cyber attacks, and has done what it can to combat such activities in accordance with Chinese law," he said in an e-mail.
Boxun has covered the Bo story, a major scandal in China, since February.
Bo, who was ousted last month, faces charges of corruption and abuse of power while his wife, Gu Kailai, is accused of killing British businessman Neil Heywood.
In the past two weeks, Meng said, Boxun has published allegations that Zhou Yongkang, China's security chief and a top Communist Party official, plotted with Bo to block the rise of Xi Jinping, slated to become China's next president, The Post reported.