The Indian Ocean tsunami of 26 December 2004 was one of the greatest natural disasters; it was also the first internet-mediated natural disaster. Despite the presumed ubiquity and power of advanced technologies including satellites and the internet, no advance warning was given to the affected coastal populations by their governments or others. This article examines the conditions for the supply of effective early warnings of disasters, drawing from the experience of both the 26 December 2004 tsunami and the false warnings issued after another great earthquake in the Sunda Trench on 28 March 2005. The potential of information and communication technologies for prompt communication of hazard detection and monitoring information and for effective dissemination of alert and warning messages is examined. The factors contributing to the absence of institutions necessary for the realization of that potential are explored.