Crowdsourcing provides un precedented new opportunities for people to share their knowledge and observations with the rest of the world. And because of their relatively high cost and low scale, more conventional, centralized means of data collection are being displaced by crowdsourced alternatives. To this point, attempts to pollute user contributed data have been rare, but this seems unlikely to remain true for long. Thus, security re searchers and practitioners alike must strive to develop better techniques and tools to help verify the authenticity of the data on which we increasingly rely.