Why is there so much secrecy between greek organizations?

[SMSUBear]

So basically, it's done just to remember what it means to be a (insert greek organization)? That makes sense. I just was with a friend of mine who was (is) greek, and I asked him a question about something, and he said. "I can't tell you that." It seemed rather irrelevant at the time, but now I see why.

Are there certain greek groups who are more secretive than others? I'm not looking for names, just wondering.

SMSUBear