Scientists discovered that tobacco mosaic virus can infect and replicate inside some fungal pathogens like Botrytis and Verticillium, which are major crop diseases. Interestingly, when viruses infect these fungi, the fungi activate their own defense mechanisms to fight the virus, yet still maintain their ability to cause disease in plants. This discovery opens new possibilities for using plant viruses as tools to study and potentially control harmful fungal pathogens on crops.