Question

is viruses are useful or harmful explain

Answer 1

yes, viruses are harmful they are disease causing microbes.
 

Answer 2

Yes, viruses are harmful, they are obligate parasite, the inert outside the whole the inert outside the whole host cell called virion.

the causes viral diseases such as plant viral diseases animal viral diseases and human viral diseases.

a biosynthetic machinery is absent in it there is no system to liberate energy and so they do not grow.

but when it enters to living body this start growing and intermediately captured the host.