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Facebook shows inbox messages publicly pre 2010
Due to a FACEBOOK glitch, private inbox messages are now visible for everyone to see - from 2009 and earlier. Check your timeline from those years. They look like wall posts but they are not!
Fix it like this: when you're in your own timeline, just click on the year on the right (2007, 2008, 2009...) ( top right hand corner by the cover picture) and you'll see a box with an amount of friends' messages and a header that says '89 (or whatever) people have written on XXX timeline' - hover over the right until you see the pencil, click and select hide from timeline. Do that for each year. BOTH parties have to delete.
Unless you want everyone to see your post-party gossip / bitching about work / social life organising / that sort of thing.