What are the characteristics of viruses?

Viruses are obligate intracellular parasites of nucleic acid and protein. Their RNA or DNA genome is covered with a protein coat. They are among the smallest infectious agents known. They range in size from the tiny polio virus (2 nm diameter) to the large pox virus, which is 400 nm in diameter.

Viruses are also looked upon as highly evolved mobile genetic elements that have cellular origin. Viruses exhibit typical morphological and physical characters including a great variety in size and shape, chemical composition, structure of the genome and mode of replication.

Viruses lack most of the enzymes necessary for the metabolism and synthesis of complex molecules and so can replicate only inside a living cell.

The strandedness of genome of a virus is a characteristic feature. The viral genome may consist of one type of nucleic acid either DNA or RNA which may be single stranded or double stranded. Viruses make us of the ribosomes of their host cells; this defined as absolute parasitism.
What are the characteristics of viruses?