Virus are living beings but it is hard to decide whether they are living or not because of several reasons.
1- they show the characteristics of living being when only it live in a cell.
2- they never breathe
3- they are minute
4- they have a simple body structure
5- they reproduce
some say they are in the border between living and non living
Viruses are not always classified as living cells because they cannot live independently. They rely on a host to provide all resources to live, without a host they are in a dormant, near dead like state. Therefore it has to define a virus as dead or alive as it may or may not have a host.
