I think it's still "All rights reserved". The rules for Ludum Dare say that you have to submit the code for judging, but you don't give up copyright. And he didn't put any license in the source archive. Although I doubt he'll complain, this porting effort might violate his copyright.
Last I heard at least, he still seem to regard mods to Minecraft as some bad terrible thing (though apparently Jeb has at least gotten him to go along with a mod framework--which is a good thing, because it's the only way Minecraft remains playable!), so "I doubt he'll complain" might be reaching a bit.
My impression was that Notch is fine with mods, but he just doesn't think there's a way to make Minecraft very moddable without effectively open-sourcing it, which he doesn't want to do.
Actually, isn't he still in Sweden? In that case, I have no idea if computer software is automatically copyrighted the moment it's written. I think maybe that's a US-only thing?
Sweden signed the Berne Convention [1] in 1904 [2], and has automatic copyright since at least then
They also signed the WIPO Copyright Treaty [3] in 2002, which expclitly says that computer programs are to be treated as literary works, and receive the same protection (that has been implemented by the DMCA in the US).
According to Directive 2006/116/EC [4] the copyright term in the EU for literary works up to 70 years after the author died.
If life expectancy continues to increase, they will probably extend the term again to cover the intended 2 generations.
Have fun playing your copy on vintage hardware then :)
