Secret Society and GLOs

I was going over my fraternity constitution and beside not being allowed to join other national fraternities, it also specifically banned membership in an organization called Theta Nu Epsilon. I decided to do some snooping around and found out that TNE is also known as Skulls and Keys, The MAchine, etc. I also talk to other friends of mine, and their constitution also forbid the membership in TNE. Just wondering why. Also I would like to know if anybody ever herd of them. They sound very secretive.