I agree I would just stick to talking about strangers and not to just trust anyone that they do not know. I would not get into the predator issue because it will be more problems for you because of how ASD kids Process things so literally.

We taught our children about rules regarding strangers. (ie. what is a stranger, don't talk to strangers, never go with a stranger, etc). Also, there's several good childrens books that teach about "private parts" and to tell a parent if someone touches them in those places.

We did not talk about sexual predators because we did not want to make our children fearful. Most autistic children are very literal. I advise caution.

I guess sexual predator's is a rather strong statement. But my son is 17 years old. And I do concern myself with this matter. Cuz, a sexual predator he had in his life was his grandfather on his biological father's side. Plus, my son's Uncle, his biological father's Uncle. So, it doesn't only pertain to strangers.
I totally understand when you both state about how our kids process things so literally.
Right now, my son is going through someone he trusted, bullied him. And he brings this up everyday. My son has limited language skills. But at the beginning of this bullying. My son just shakes by the mention of this person's name, put my son into anxiety.
I keep on letting my son know, that I am there for him. And that person is not allowed to come over again. But now my son has acted out what had happened to him. Again, I am constantly reassuring him.
So now, how do I go about all this, when the people my son trusted in his life mark him as a target?
I am starting to feel I let my son down....

You can't take ownership for the evil acts of others. However all parents should do whatever they can to protect and prepare their children. And be there for them when it still goes wrong.

For our kids that have limited language, we should arrange their lives so they always have someone near that can protect them (from bullying, mistreatment, crimes, etc).... just like we do for our children when they are young. I know is very difficult but I only have trusted people care for my son. And my son is in a self-contained classroom with a 1-on-1 aide. I don't know if you can arrange this for your child as well. I assume that you would never leave your child alone with a known sexual predator even if that person is related. In fact, is there a reason why your son would ever need to be around those relatives?