GitHub is one of several major firms that has been the victim of cyber attacks over the last few days.
“We are currently experience the largest DDoS [distributed denial of service] attack in GitHub’s history,” wrote the firm’s systems engineer Jesse Newland in an official blog post. "Based on reports we’ve received, we believe the intent of this attack is to convince us to remove a specific class of content.”
The content Newland refers to is believes to be web pages that provide users from China with ways to circumvent censorship controls for the region.

http://www.mcvuk.com/news/read/githu...attack/0147347