See the GPL FAQ http://www.gnu.org/licenses/gpl-faq.html#MereAggregation http://www.gnu.org/licenses/gpl-faq.html#MereAggregation The last paragraph describe t

See the GPL FAQ http://www.gnu.org/licenses/gpl-faq.html#MereAggregation http://www.gnu.org/licenses/gpl-faq.html#MereAggregation The last paragraph describe the gray area; i.e. if a proprietary program depends on- and combine a GPL program to perform its functionality it can be argued that the two parts are a combined work and hence the whole work must be licensed under the GPL.