I have tried to search for this answer for quite some time and I have gone through all the various FAQ's and documentation regarding the three licenses; but none of them have been able to answer a question that I have. So I've been working an idea for a website for sometime now and recently I found open source software that has many of components that are similar. It is licensed under the mpl/gpl/lgpl licenses. I think for the most part I understand the ramifications, due to the searches and reading, of what is required if I modify/use and want to distribute the software. But what if I want to modify and not distribute, but use it on a public website that I generate ad revenue from? Is this illegal? It doesn't seem like it is from reading other open source system, say like Drupal, where they allow you to use the software but it's not considered "distribution" if people just go to the website. I know this site may not be the best resource and I've tried some other sites, but I haven't received any clear replies back. If you know some other resource that I could contact also, please let me know. Links for those who don't know: MPL - Wikipedia, Legalese GPL - Wikipedia, Legalese LGPL - Wikipedia, Legalese