The DNA sensor, cyclic GMP-AMP synthase (cGAS), is essential for the detection of viral infection. In a recent issue of Science, two studies, Bridgeman et al. (2015) and Gentili et al. (2015), report a novel mechanism for propagating an antiviral signal between cells, based on the transfer of the cGAS enzymatic product, cyclic GMP-AMP (cGAMP), in viral particles.