hercules1 - "asked him again to get rid of the sodding msn from our pc."
You're not alone - I've a client whose son (own PC in his bedroom, but no working mouse) seems to put MSN onto any machine he lays his hands on... Dad's PC, then the old laptop, then Mum's new laptop... they're sick of it too, and I just rename it (so msn.exe becomes msnx.exe and he gets "not found") but I've not gone as far {yet} as making www.msn.com fail to load completely on their PCs... but that's next if they get fed up again!
Certainly (on the issue of family squabbles {from no reason at all} being shared on FB) it does seem that privacy settings are a big issue, and stressed time and again - guy from Google said "OK, Google isn't a 'social network' but it is good at finding information" He said he'd impressed on his children not to put anything personal online, and that if they did it would turn up to blight their future career or university entrance...
Those drugs/booze parties, or nude pix on the beach, or whatever, are enough to block someone years later when they had put the activity out of their mind, hoping for some new job or entrance at a prestigious university...
Of course, there's also the possibility that some leave their FB pages open for anyone to rub in any "I've stolen X's BF/GF" and get some minor fun from it for a couple of weeks, exchanging snide remarks/threats.