Retroviruses
A retrovirus is a virus with an mRNA based genome. They use their own Reverse transcriptase from within their capsid to convert their viral mRNA genome to cDNA that can be integrated into the hosts genome via an integrase enzyme which acts akin to a transposon. This results in the host inadvertently duplicating the virus. The term 'retro' stems from the fact that the virus has reversed the usual flow of DNA to RNA .