The source can be from emails, email attachments, bots, Trojans, and other sources that can be introduced via any computer file type from any device type including all forms of mobile devices, the cloud, the web and even via a virtual private network (VPN).
Three possibilities proposed by Cox: a "peer-to-peer" social network, a cluster of "virtual individual servers" running on a cloud service such as Amazon Elastic Computer Cloud, and "hybrid decentralization, " a mix of the two approaches.