Share-alike

Two currently-supported Creative Commons licenses have the ShareAlike condition: Creative Commons Attribution-ShareAlike (a copyleft, free content license) and Creative Commons Attribution-NonCommercial-ShareAlike (a proprietary license).

The term has also been used outside copyright law to refer to a similar plan for patent licensing.

These licenses have been described pejoratively as viral licenses, because the inclusion of copyleft material in a larger work typically requires the entire work to be made copyleft.

According to Creative Commons, the advantage of this license is that future users are not able to add new restrictions to a derivative of your work; their derivatives must be licensed the same way.

Over the years, Creative Commons has issued 5 versions of the BY-SA and BY-NC-SA licenses (1.0, 2.0, 2.5, 3.0 and 4.0).