>That's what I was thinking. However, is it copyright infringement to >take up the last GPL'ed version of the software, modify it and release >it under GPL? Of course, the original copyrights would remain intact >and be distributed with it.
If you receiveed (or downloaded etc) a copy of the code with the GPL license in effect, you can continue to use that code under the license terms that were given to you (gpl in this case). If, for some reason, you were to get the same code, but not under the gpl, then you could not redistribute that code as gpl. Telling the difference, of course, might be difficult. Carl