Originally Posted by p_paira
It's stock launcher how would you seen ads in this..?
It is mostly caused by sideloading app from obscure site. It tends to trick you to install a fake app disguised in a similar file name. When you press install it has no icon and has different name which frequenly slipped from attention. Just scroll to the bottom of listed apps until you'll find one with no icon, simply uninstall it and you'll be fine. In rare case, a device admin permission was given to it, it will be harder to remove. In this case, reboot to safe mode and uninstall the annoying app.