Message with dismiss button saying "Ive been watching you I know everything" it wasn't a normal sms it Diddnt have no name or number

I was walking back to work the other day and my phone had vibrated I looked at it and it had a pop up sort of message saying "ive been watching you. I know everything. it only had a dismiss button at the bottom of the screen i screen shotted screen and have attached it below, I have not received any more of these messages 35 204806 472172 6