A recent paper on characterizing endogenous retrovirus sequences has attracted some attention because of a press release from Kyoto University that focused on refuting junk DNA. But it turns out that there's no mention of junk DNA in the published paper.
Let's start with a little background. Retroviruses are RNA viruses that go though a stage where their RNA genomes are copied into DNA by reverse transcriptase. The virus may integrate into the host genome and be carried along for many generations producing low levels of virus particles [Retrotransposons/Endogenous Retroviruses]. The integrated copies are called endogenous retroviruses (ERVs).
Our genome contains about 31 different families of ERVS that have integrated over millions of years. Most of the original virus genomes have acquired mutations, including insertions and deletions, and they are no longer active. These sequences account for about 8% of our genome.