I knew that some nitpicker would discuss exactly this phrase ;) It's the appstore that "you are using", or the appstore that is "installed on your phone", in case you don't know what I'm referring to, otherwise.
Sort of, because I'm sure he/she knew exactly what the title was referring to ;) Anyway, that's not really important. By the way, it affects Android, iOS, Windows Phone and Blackberry -- what platform are you using then?