A real online university will have an actual campus somewhere, usually more than one somewhere.

A real online university will be accredited by at least one higher education accrediting agency.

A real online university will be registered somewhere and will have several years of existence. Often they will be associated with a physical university if they aren't acuatlly a branch of that university.

A real online university will teach valid college courses. If they offer things like astrology, handwriting analysis, and the like and don't offer math, science and the like, they are probably fraudulent.

I am registered to start attending National American University as of November 30, 2005. They have a number of physical campuses and have been in existence since 1941. The do also offer online courses.

This is just one example of one that is real. There are others as well.