Mass has energy then ? shouldn?t all energy has mass?

Humm.. If all mass has energy then counter ? shouldn?t all energy has mass? A Photon, I believe, is the most prolific energy/ mass/ wave/ frequency in the universe. There is arguably no space in the universe that isn?t filled with photons going hither and to. Are photons the illusive dark mass the scientist have been searching for but can?t ?see? because there isn?t something there to absorb the energy?