The ICPSR web server was unavailable between 10:51am and 11:11am EST on Saturday, March 6, 2010.
During this time the ICPSR web server had limited availability due to a denial of service attack from an IP address belonging to a broadband network provider in China. ICPSR technical staff applied a temporary fix by denying access to the web server for that IP address. University of Michigan networking staff later applied a more permanent fix by updating access control lists within the university network.
ICPSR is in the process of adopting a centrally managed "virtual firewall" service from the University of Michigan, and that will make it faster and easier to respond to attacks such as these.