samsung gs 3 has a window that keeps popping up

[AC Question]

My moble has been acting weirdly since yesterday. A window keeps popping up every five to ten minutes. It usually a white blank page with an 'X' option. Sometimes it opens says that it cant open a link (which I don't open and doesnt copy when i try to)
its veey annoying and I dont know what to do to stop it.