According to Apple's product page, the Airport Extreme...
"...can turn your external USB hard drive into a secure drive you can share across your Wi‑Fi network and access securely over the Internet."
My interpretation of the "access securely over the Internet" part is that if I plug in an external hard drive to an Airport Extreme on my home network, I can get to it from anywhere via the internet... including outside of my home network.
Am I interpreting this correctly? If so, it sounds like a pretty awesome feature! I guess I'm skeptical though because when I Google around for this, I find nothing relevant... including any info from Apple. What gives?