An international group of scientists this week ended a year-long moratorium on controversial work to engineer potentially deadly strains of the H5N1 avian flu virus in the lab. Researchers agreed to temporarily halt the work in January 2012, after a fierce row erupted over whether it was safe to publish two papers reporting that the introduction of a handful of mutations enabled the H5N1 virus to spread efficiently between ferrets, a model of flu in mammals (see Nature http://doi.org/fxv55r; 2012). Both papers were eventually published, one in Nature1 and one in Science2. Now, in a letter simultaneously published on 23...