From The Committee for Protecting Journalists website:
Change.org is back up and running after what the site said was a cyberattack that came from within China. Here’s the site’s announcement that was running on its homepage earlier today:
Change.org is currently experiencing intermittent downtime due to a denial of service attack from China on our web site. It appears the attack is in response to a Change.org petition signed by nearly 100,000 people worldwide, who are standing against the detention of Chinese artist and activist Ai WeiWei. Despite this attack on our members and our platform, we will continue to stand with the supporters of Ai Weiwei to defend free speech and the freedom to organize for people everywhere. In the meantime, we apologize for any inconvenience.