At some point, determined by how the virus was programmed the virus attacks.
只有在某个点上病毒程序才会发作（这是由病毒程序的设计所决定的）。
The direct cause, such as a bacterium or virus, of a communicable disease.
传染原传染性疾病的直接病因，例如某种细菌或病毒
Scientists have isolated the virus causing the epidemic.
科学家们已分离出引起这种流行病的病毒。
