Flu viruses cause disease, they cause influenza (flu). They are the infectious agents of the flu. The viruses are submicroscopic organisms that infect your body and that give you the influenza, the disease.
No. Computer viruses are only called "viruses" by figurative analogy with biological viruses. And biological viruses (such as chickenpox, hepatitis, and the flu) are not the same as disease-causing bacteria (such as strep throat, tuberculosis, and lyme disease).