From NIN.com it's a legal, high-quality, MP3 download (about 8 MB) with track artwork embedded. You supply your e-mail address and zip/postal code and they send you a download link:
http://dl.nin.com/discipline/nin
It's a friggin' solid track. Also, the comment in the file info for the MP3 says: "Go to www.nin.com May 5".
Trent Reznor/NIN continuing to do good stuff!
[Edited: subject line to include album; as of May 5 you can download the full album from www.nin.com]