Yes you can play offline single players perfectly fine. It does need for you to attempt to login to the server first but if it fails the offline option button appears. There might even be a way to mod the client so the offline button is there from the start, I'd have to look that one up though.

You have to login once to verify your account, after that you can play offline.
And if you backup the directory you've got your offline version.

Thanks for this discussion, because I was supposed to buy Minecraft as a gift to someone, but first I wanted to know what kind of DRM, if any, it has.

So if you re-install the game years from now to another PC (using the backup directory if needed), it will not require another authentication?

To be honest, I haven't actually tried it.
I know you can remove the directory and put your backup back and play offline.
And I know that if you remove the 'lastlogin' file you can't start it up anymore since your credentials are gone.
And I didn't see any registry entries when I did a (very) quick check, so I assume it should work.
Unfortunately I don't have two working computers right now so I can't try it out.

MC is a game with always online DRM and a restricted offline demo mode.
You know what really gets me though because it's MC and "indie" people don't care when Ubi or EA do it well thats just wrong!!!!!111one. I won't add blizz or Valve there as people are apparently ok with them doing it -.-

http://i.cubeupload.com/KMYQZW.png

Notch donated after #2

Java is DRM in itself (yea, I know I would get bashed for saying that). :)

Well... I do genuinly think that in case of Minecraft it's not as much of DRM as honest inadequacy on the side of devs, Notch namely since he's the one who made base code. The very decision to use Java for something like Minecraft would prove that.

Wait what, how is the offline mode a demo mode? Also, the 'online mode' only requires login at start up, so that's hardly always online.

I played MC in offline more for more than 100 hours, only going online to update it, and I copied it without issue to another computer without having to reactivate it or be online.

So unless they changed something very recently I would hardly call that "always online DRM", it's not as good as having a full "DRM-free" installer but, for me at least, it's good enough.

How is the offline version a restricted demo mode ?

You need a one time connection to the server using your account credentials, after that you can play Minecraft forever on a machine without internet. How is that always online DRM ?

The game doesn't even actually require activation as such. That first log in is the downloading/installation of the game. Once it's downloaded, you can freely back up and move those files to any computer without having to log in again. If the game really required activation it wouldn't work when you copied it to another computer.

I think part of the problem is that Minecraft is at its core a multiplayer game. One the JAR is downloaded you can actually archive that file and copy it and play it to your heart's content in single-player game. So in the most literal sense, Minecraft is DRM free.

However: unmodified Minecraft servers require clients to have authenticated via minecraft.net beforehand. I fell foul of this as we had a LAN party without an internet connection some time ago. We wanted to get a local Minecraft server up and running, and the server itself did work, the local Minecraft clients could not connect because they needed to authenticate with minecraft.net first. Obviously - no internet, no authentication.

So Minecraft is not DRM-free for multiplayer purposes. There are cracks in circulation ("private servers" I believe they're called) that circumvent this, but vanilla Minecraft does have DRM, something which is greatly at odds with Notch's statements and PR activities.

I'll be damned. Later today I actually got a SMS about buying Minecraft (as a gift). It would come to two kids (in the same household), so now it is a bit unclear at least to them whether buying one copy is enough, or if both have to have a copy of their own? If we are speaking about single-player only.

If I understood the discussion above, one copy is fine for single-player game, but if they want to play multiplayer (e.g. together), then both need a copy of their own. Piracy is not the correct answer to this, either.

Maybe I'll buy one copy first and see it they are happy with it.