Random advertising on home screen of Galaxy S4


Don't know why but all of a sudden every now and then I seem to get a box on the home page of my Galaxy S4. The most common one I'm getting is
'Win an iPad' etc

Anyone got any ideas on what is causing this
p.s. I only have limited apps etc on phone, the basics Social Media, Daily Mail, Navigation etc nothing in the way of games that may have virus's sitting behind them etc etc

Any help would be appreciated