The packages that started arriving by FedEx on 12 October last year came with strict instructions: protect the information within and destroy it after review. Inside were two manuscripts showing how the deadly H5N1 avian influenza virus could be made to transmit between mammals. The recipients of these packages ? eight members of the US National Science Advisory Board for Biosecurity (NSABB) ? faced the unenviable task of deciding whether the research was safe to publish.