According to the Virology Blog -
"About eight percent of human DNA is viral: it consists of retroviral genomes produced by infections that occurred many years ago. These endogenous retroviruses are passed from parent to child in our DNA. Some of these viral genomes are activated for a brief time during human embryogenesis, suggesting that they may play a role in development.
There are over 500,000 endogenous retroviruses in the human genome, about 20 times more than human genes. They were acquired millions of years ago after retroviral infection. In this process, viral RNA is converted to DNA, which then integrates into cell DNA. If the retroviral infection takes place in the germ line, the integrated DNA may be passed on to offspring."
It should be noted that the common cold is a retrovirus.
Thanks! That helps, or at least adds complexity, when trying to put the human DNA percentage comparisons with other species into sharp perspective.