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.