It's blatantly irresponsible that SSI even has the infrastructure to burn CDs with this information on it (it needs to live in heavily secured, jealously guarded and scrupulously audited (ideally airgapped) computer system). If they absolutely need this capability, it's blatantly irresponsible to let such a CD out of the care of trusted employees -- and if they absolutely need to post it, they need to heavily encrypt it.
It's not meaningfully "the post service's fault".