Viruses are masters at taking over our cells: They disable our defenses and hijack the cellular machinery in order to multiply successfully. For example, the herpes simplex virus 1, which causes blister-like skin rashes, and influenza viruses specifically block a crucial step in gene activity in which the production of RNA molecules is completed—known as transcription termination. The blockade results in unnaturally long RNA molecules that cannot be translated into proteins. This suppresses the antiviral defense in the cells and creates optimal conditions for the viruses to multiply.