While originally intended to “underscore the dilemmas and concerns that people would face if they relied too heavily on the new communications infrastructure,”[1] Stand Alone Complex eventually came to represent a phenomenon where unrelated, yet very similar actions of individuals create a seemingly concerted effort. A Stand Alone Complex can be compared to the copycat behavior that often occurs after incidents such as serial murders or terrorist attacks. An incident catches the public's attention and certain types of people “get on the bandwagon”, so to speak. It is particularly apparent when the incident appears to be the result of well-known political or religious beliefs, but it can also occur in response to intense media attention. For example, a mere fire, no matter the number of deaths, is just a garden variety tragedy. However, if the right kind of people begin to believe it was arson, caused by deliberate action, the threat increases drastically that more arsons will be committed. What separates the Stand Alone Complex from normal copycat behavior is that the originator of the copied action is not even a real person, but merely a rumored figure that commits said action. Even without instruction or leadership a certain type of person will spring into action to imitate the rumored action and move toward the same goal even if only subconsciously. The result is an epidemic of copied behavior-with no originator. One could say that the Stand Alone Complex is mass hysteria-with purpose. This is not unlike the concepts of memes (refer to the conversation between the major and the Puppet Master in the manga) and second-order simulacra. It also has ties to social theory, as illustrated in the work of Frederic Jameson and Masachi Osawa.

http://en.wikipedia.org/wiki/Ghost_in_the_Shell_%28philosophy%29#Stand_Alone_Complex