What’s more, since viruses are frequently classified as nonliving, many types of viral infection — especially when viruses successfully colonize a host in a persistent, lifelong manner without causing acute illness — are ignored as “backwater” science, says Villarreal. For example, a DNA virus called polyomavirus is commonly used in laboratories to study how viruses cause cancer. Scientists may always dispute whether viruses are alive or not, but they can hopefully agree on the importance of viruses to life as we know it.