Through downloading from the exchange you can get a whole mess of free stuff, which is always nice. Howevers, sometimes THE BAD STUFF can also end up in your game. No one wants that.
So, if you ever see any deformed toddlers, naked Sims, or men with boobs wandering around your neighbourhood, look out for these things-
Metallica Magnets logo t-shirt
night time and day time everyday shoes
toddler_tee (with 'milk' written on it)
collectionblondes (has a picture of a woman with a black bikini top and bottom)
If you go into the installed content section of your launcher and see any of those items in the list, run for your life! Or alternatively just uninstall them and everyfink should be grand again. But maybe you like your game with a bit of spice in it? In which case, by all means keep the freakz.