You're on Facebook, reading something, when suddenly 'Congratulations! You've won ______' pops up. Annoying, but also dangerous. It's FAKE 'you won' malware.
First, DON'T CLICK ON IT! Close out (don't click on the close x they give you) but rather, swipe out of whatever you were in.
Then, clear out your phone's history by going to safari in settings, for example. Even better, do a 'factory reset' but be sure your info is backed up first.
MORE TIPS HERE and in the video below!