Everything is virus: one of the theories of how cells went from RNA to DNA is viruses.

Forterre (2006) proposed that early cellular lineages diversified while still harboring RNA genomes, with viruses and cells coexisting from the beginning. In his model, the first fixation of DNA occurred in viruses, which subsequently transferred the enzymes necessary for DNA synthesis and maintenance into independent cellular lineages. Thus, RNA genomes in ancestral cells were converted into DNA genomes via viral intermediates (Forterre, 2002, 2006). The structural and functional differences among cellular replication systems would then reflect the independent viral origins of DNA replication machinery.

https://www.sciencedirect.com/science/article/abs/pii/S0303264725002813