From Repair Mobile
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The BSD License Problem
The two major categories of free software license are copyleft and non-copyleft . Copyleft licenses such as the GNU GPL insist that modified versions of the program must be free software as well. Non-copyleft licenses do not insist on this. We recommend copyleft, because it protects freedom for all users, but non-copylefted software can still be free software, and useful to the free software community.[1] - thanks to gnu.org More details.
