We are currently experiencing the largest DDoS (distributed denial of service) attack in github.com's history. The attack began around 2AM UTC on Thursday, March 26, 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. Based on reports we've received, we believe the intent of this attack is to convince us to remove a specific class of content.
We are completely focused on mitigating this attack. Our top priority is making sure github.com is available to all our users while deflecting malicious traffic. Please watch our status site or follow @githubstatus on Twitter for real-time updates.