Weird message appeared, like spam, black screen, green button? Yesterday I received a weird message on my iPhone 4, it was a completely black screen with a wide green / standard button at the bottom. 

It seemed like a kind of broadcasted message.

The message said something about RSVP.

I've never seen a message like this before, wasn't an email, SMS or iMessage. I did a search on Bluetooth apps to see if I could see this type of thing, but didn't find anything. 

I dont know if its related, but a few minutes later I heard a sent message noise.

I can't find the message in texts or email either.

It all feels like I've been hacked into some how.
That's an operator message which gets displayed directly on the screen and doesn't get added to the usual SMS messages. My bank uses them to send me the login PIN for electronic banking whenever I want to log in.