The present article draws from fieldwork on the indignados (or 15M) movement in Spain to propose a new approach to the study of protest movements in the digital era: ‘media epidemiography’. This composite of the terms ‘epidemiology’ and ‘ethnography’ is used as a heuristic to address the research challenge of today’s swiftly evolving techno-political terrains. I argue that viral media have played a key role in Spain’s indignados movement, with Twitter as the central site of propagation. Protesters have used Twitter and other viral platforms to great effect and in a range of different ways, including as a means of setting the tone and agenda of the protests, spreading slogans and organizational practices, and offering alternative accounts of the movement. These developments may signal the coming of an era in which political reality is shaped by viral contents ‘shared’ by media professionals and amateurs – an age of viral reality.