I heard that Corona is getting all of the gang bangers from LA moving there due to the cheap housing. What I know about Corona I remember from a quick drive-through about five years ago (I stopped at a Safeway there). I'm sure there are some nice sections there however, as it is a pretty big place.
I haven't seen 'em. Not in Corona. Central Corona (actually North Corona) has its fair share of illegal aliens and anchor babies, but I haven't noticed any uptick in gang activity here. I've been here 20 years and I still don't lock my door.