Bats may have passed on a virus that led to SARS. A bat coronavirus shows signs of being a mix of different viruses, suggesting it could be the ancestor of the SARS virus. This new finding points to a specific bat species as the likely source of the SARS outbreak. The transfer of this virus from bats to another animal, like civets, likely happened around 4 years before the SARS outbreak. This information helps us understand where SARS came from and where to focus future research.