From what I gather it's bag type slings. These slings are worn around the parents' neck and body much like a messenger bag is worn. Baby is placed into a deep pocket in these slings and so is at risk for suffocation because their bodies are positioned in a C position where the child's neck often touches their chest and restricts airways. All the while, the poor mom or dad wearing baby could be oblivious to any danger because baby is all the way down by mom or dad's belly button.
Baby-wearing safety points to remember are:Baby should be close enough to kiss.
Baby should never have his chin resting on his chest.
Baby's head should be above the rest of her body.
Baby's knees should be higher than his butt.
Baby's face shouldn't be covered by fabric.
Baby's head should be supported.
I was actually given one of these types of slings to use when DD was weeks old. I'd read about some slings not being safe, but had no idea which ones at the time. Something just didn't feel right when I put her in it though and I only ever tried her in it twice and that was literally put her in and take her out.
I also had a Babasling my SIL gave me, but most of the time I struggled to get DD in a position I was happy with in that too. And she outgrew it lengthways before I could put her in a position she could support herself in. That despite the fact I asked my SIL to get me a ring sling
My heart goes out to those parents who have lost LO's when all they've been trying to do is the best thing for them. I hope it makes for people becoming better educated about baby wearing and looking to things like sling-meets for advice and to try before they buy.