So that .Spotlight-V100 store some kind of index, probably binary. I presume that any Mac reads it on any arbitrary USB drive it's plugged in (or, at least, when a search is triggered). By creating a specially-crafted, corrupted index I see a channel for denial of service attacks.
You can probably still abuse NSDictionary, causing HashDoS (https://gist.github.com/dchest/4467707). I did it with QuickLook a few years ago; don't know if they replaced a hash function there.
