My Lock Screen was hacked and a picture of a bearded guy flicking me of with a "FU!" caption.

This morning I woke up to see a foreign picture on my Lock Screen. The picture was a bearded guy with the US flag draped around his neck and his middle fingers up and the caption "FU!"..

After opening my phone it seemed normal but, when I locked it again I saw the same picture.

My original lock screen image was faded to the background and this square picture was centered on the screen.

After a few more tries to lock-unlock the picture disappeared and my Lock Screen remained faded.

I restored my phone to a backup from 3 days ago and it seems to be normal now but..

How did this happen?

Apple Support was great and took me through clearing Safari history and blocking popups but, there was no answer to the question: How did this happen?

I'm still very concerned..