Annoying ads

[Turtell]

I have been getting very annoying, full screen ads frequently when I first swipe open my phone.  Also at other times.  There is also a frequent small "yo-yo" ad that drops down from the upper right.  The Verizon store people have no idea where these come from.  Is there an app I can delete or setting I can change to get rid of these?  They are often timed to pop up just when I am selecting something and then hit the ad instead, thereby opening it.  Thanks.