China has been identified as the source of the attack and the software being hit is banned behind the bamboo curtain. It would appear that someone is taking pro-active censorship steps by taking down the entire site..
"Eighty-seven hours in, our mitigation is deflecting most attack traffic. We're aware of intermittent issues and continue to adapt our response," a tweet from the GitHub
The site's blog said the flood of Internet traffic to GitHub came from Chinese search engine Baidu targeting two GitHub pages that linked to copies of sites that are banned in China.
GitHub said that the attack began early on Thursday "and involves a wide combination of attack vectors."
"These include every vector we've seen in previous attacks as well as some sophisticated new techniques that use the web browsers of unsuspecting, uninvolved people to flood github.com with high levels of traffic," the blog post continued.
"Based on reports we've received, we believe the intent of this attack is to convince us to remove a specific class of content."
GitHub supplies social coding tools for developers and calls itself the world's largest code host.
A Baidu spokesman said the company had conducted a thorough investigation and found that it was neither a security problem on Baidu's side nor a hacking attack.
"We have notified other security organizations and are working to get to the bottom of this," the spokesman said.