The legions of speculators, investors, and commentators who look for exogenous causes of stock market movements will perhaps say that WannaCry was dismissed because the damage was limited. However, the reported number of computers that have been affected rose all day, and there were news stories that at least one variation of the ransomware had no kill switch, which means it could proliferate unchecked. So during the trading day, nobody really knew how bad the damage was or how bad it would get. Also, while all the implications for computer and network security are not fully known, this incident, the worst of its kind so far, is a loud and clear warning of proliferating risks. Those risks are especially worrisome for companies whose business models depend on computers and the internet.