These questions came up recently after a hosting provider, Appnor, took an application that had been under the GPL and, after obtaining consent from the original developer and paying for the rights, released it with his own changes under a proprietary licence.
Appnor's Dragos Manac came in for a shellacking from the ferals who infest the American news accumulation site Slashdot after news of what had happened was posted on the site a couple of days ago.
Manac had obtained the rights to WinMTR, a port of mtr, a tool for testing networks. It combines the functions of ping and traceroute in a single diagnostic tool.
WinMTR had been developed by Vasile Stanimir, a friend of Manac's. The project was at a standstill for some years, he claims.
Manac said in a posting on his blog: "Since the project was no longer being developed, I offered to buy the rights and offer it for free, on behalf of Appnor. So I bought the rights."
His intention was to offer WinMTR as freeware under a proprietary licence. "After 3 days (actually nights) of reflecting on it, I decided to revoke the GPL since we had full rights. There was only one external contribution, a broken patch from 2001 that got removed. Nobody went through the trouble of adding new features in a decade, but there were many feature requests."
But he was not prepared for the storm that erupted once this news was posted on Slashdot, referencing a post by an open source developer, Philip Paradis. A respondent to the post on Paradis' blog pointed out some lines of code which were believed to be from the original mtr and which, could, therefore mean that Manac was violating the GPL.
"I strongly believe that we are entitled to change the license. But to what effect? An angry mob. The comments on Slashdot prove that; A good story for our competition; (and) a very long list of debates and arguments in which we have to prove that we are not creeps," Manac wrote.
He has now released the code for WinMTR under the second version of the GPL. It seems unlikely that he had any bad intentions.
A well-known free software advocate and GPL expert believes that all the inaccuracies could be explained by confusion on Manac's part, not malevolence.
Bradley Kuhn told iTWire: "It's true that one can choose to cease distribution under the GPL: that's fine. Indeed, no one is required to continually distribute something under the terms of the GPL; they can stop whenever they want."
Kuhn added: "However, there is a very important distinction between 'not distributing anymore under the GPL' and 'revoking the license of those who already received copies under GPL'.
"Everything I've just read about this story appear to confuse these two issues completely, including Dragos' own blog post and those responding to him. I can't even figure out which of those things he intended to do in the first place.
"In fact, we'll probably never know what Dragos intended to do here, since he's now said that he will make the code available under the GPL himself again. It therefore seems like a non-story to me at this point."
Kuhn said that, to his knowledge, the GPL was an irrevocable license. "Once software is legitimately released under the GPL, everyone who received a copy under the GPL has rights to copy, share, modify and/or redistribute that software under the terms of the GPL.
"Meanwhile, if the copyright of the original version was held by a single person or entity, they can of course relicense *that* version another way, and stop releasing future versions of their own under the GPL."
Asked about projects which had multiple people contributing code under the GPL, Kuhn said it was possible to relicense code in this case too, provided that there was universal agreement of all copyright holders.
"If no copyright assignments are in place, the only permission anyone has to make and distribute the work is under PL. Each patch sent in by a contributor is typically a derivative work (IANAL, but that's what lawyers have told me)," Kuhn added.