I have written a commercial application which contains closed source code and a script API which is open source. Currently I have a CLA similar to this which has to be signed by each contributor to be able to make changes/updates to the script API. However I'm not quite sure under which license I should release the public script API source code? The code belongs to me (copyright) but users should be able to use the code to design and distribute plugins for free or commercially, however I would like some legal protection in case someone decides to use the script API code and turn it into something evil/illegal/copyright infringement.
My question is if there already exists a license which suits my demands?