My 10-year-old DD has just set up a Snapchat account having been told how to do so by her friend. I had heard of Snapchat, but knew nothing about it until a bit of googling just now, from which I gather that it's a way of sending photos and messages and that it is popular because you can set it for your message to "disappear" after a short length of time. I have also learnt that the message/photo may not disappear because (a) the recipient may take a screen shot of it and (b) the data is still there to be retrieved by those who know how to do these things.
According to my DD, people can only send her messages if she has given them her details. Is that correct? Or is it the case that (like e-mail) a user may receive spam from someone to whom the user has never given her address.