ANCIENT VIRAL BITS AND PIECES. “By far the dominant type of nongenic DNA are transposable elements (TEs), including various well-described retroelements such as Short and Long Interspersed Nuclear Elements (SINEs and LINEs), endogenous retroviruses, and cut-and-paste DNA transposons.”
http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1004351