I'm 47 married 20 years with 2 kids. One is 15 the other 20.
About a year ago my wife told me that my daughter had a boyfriend that lived in another state and he was moving to our state to be closer to her.
Through the course of conversation it turns out that my wife had 'found' this guy for my daughter through one of her chat rooms (movie download site). She had chatted with this guy for 2 years and never told me about it.
Well he came down and he and my daughter started dating. He later moved back to his state but they are still seeing each other occasionally.
My wife didn't seem to think there was anything wrong with the secret conversations because it was about my daughter not her.
I can tell you that I would never engage in that same behavior for my son. It seem intuitive to me not to secretly talk to a 20 year old woman about anything for 2 years or 2 days.
Hell I would be going off my face if the missus hooked my little angel up with some 'mysterious stranger dude' who I didn't have the chance to case out and have an interrog... I mean, have a 'friendly interview' with.
She's your kid too after all. Have you talked to her about this?
Maybe they both thought you would scoff at the idea of meeting someone online, so they just didn't want to tell you about it for fear that you would make them feel ridiculous. Have you expressed anything like this toward online chatting services?