Last week, Chinese hackers targeted GreatFire.org in a DDoS attack, and now are attacking GitHub. DDoS stands for "Distributed Denial of Service," and this attack brings down a website by hitting it with lots of bogus requests from thousands or even tens of thousands of computers distributed all over the world. GreatFire.org was spending $30,000 a day in bandwidth trying to keep up with the excess traffic.
The way they are getting this to be a distributed attack is by commandeering users of Baidu, a popular search engine in China.
Read more on this story from the Wall Street Journal at WSJ.com.