Sunstein co-authored a 2008 paper with Adrian Vermeule, titled "Conspiracy Theories," dealing with the risks and possible government responses to conspiracy theories resulting from "cascades" of faulty information within groups that may ultimately lead to violence. In this article they wrote, "The existence of both domestic and foreign conspiracy theories, we suggest, is no trivial matter, posing real risks to the government's antiterrorism policies, whatever the latter may be." They go on to propose that, "the best response consists in cognitive infiltration of extremist groups", where they suggest, among other tactics, "Government agents (and their allies) might enter chat rooms, online social networks, or even real-space groups and attempt to undermine percolating conspiracy theories by raising doubts about their factual premises, causal logic or implications for political action." They refer, several times, to groups that promote the view that the US Government was responsible or complicit in the September 11 attacks as "extremist groups."