Facebook privacy settings...?

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You hear cases of people tragically being killed or raped because they accepted some sort of weird, random stranger on Facebook, told him/her to meet them somewhere, and it ends horrifically.

But if you're like me, having the huge majority of Privacy Settings on 'Only Friends', and never accepting total strangers, can anyone in the world see what's on my Wall? Even though everything is 'Only Friends' (and I know these people), is there a chance that some technology whizz-kid hacks into the system and can see my Wall posts? Is 'Only Friends' really as it says?

Thank you.