Hello Neetu,

Viruses are usually characterised by three negative properties, namely, invisibility by ordinary microscopic methods, failure to be retained by filters impervious to well-known bacteria, and inability to propogate themselves in the absence of susceptible cells.

Virus classification is the process of naming viruses and placing them into a taxonomic system similar to the classification systems used for cellular organisms.

Viruses are mainly classified by phenotypic characteristics, such as morphology, nucleic acid type, mode of replication, host organisms, and thr type of disease they cause.

Hope it clears your doubt.

Thank you!