Some hacks are in compressed folders and when I open them, it says "Invalid File Types" etc. etc. etc. etc. and I think the file extension should be added so that we can download them.
There's nothing wrong with the attachments. It's just that vB3 uses a different way of linking to attachments - instead of basing it on the postid, attachments now have an attachmentid.
Therefore, old links to attachments will NOT work anymore.
Actual attachments in posts will still work, just NOT links.