Den 30-12-2011 05:02, Tim Starling skrev:
You can modify GPL software for private use. That clause only kicks in when you "distribute or publish" the work, so you're generally OK if you're just using it within a single company. Maybe that's what Huib meant by "closed source".
"distribute or publish" covers wen you put your additions for download, or otherwise gives away copies.
You can do any additions, keep it on your own servers, and sell the result to clients.