$q,$ operating systems use code that is proprietary and kept secret to prevent its use by other entities. A $$ Open$-$source B $$ Closed$-$source C $$ Freeware D $q,$ Malware $q,$ operating systems use code that is proprietary and kept secret to prevent its use by other entities. A $$ Open$-$source B $$ Closed$-$source C $$ Freeware D $q,$ Malware $q,$ operating systems use code that is proprietary and kept secret to prevent its use by other entities. A $$ Open$-$source B