Ditto in Finland. Just like in Denmark, the social security number is being used for authentication by some actors, even though it's inherently insecure to do so. The Swedish way of handling those numbers seems more reasonable; they're just used as unique identifiers and you still need to show some other kind of ID.

When I lived in Denmark, airlines occasionally did identity spot checks on domestic flights. I was always horrified to notice that everyone just pulled up (picture-less) social security cards and used them as identification.