1) Conniving 2) Covert 3) Involving collusion 1) Conniving 2) Covert 
• (a.) Characterized by collusion; done or planned in collusion. • (a.) Acting in collusion.
Col·lu'sive adjective 1. Characterized by collusion; done or planned in collusion. ' Collusive and sophistical arguings.' J. Trapp. ' Collusive divorces.' Strype. 2. Acting in collusion. ' Collusive parties .' Burke. -- Col*lu'sive*ly
[adj] - acting together in secret toward a fraudulent or illegal end
collusive 1. Acting together in secret toward a fraudulent or illegal end. 2. Secretly cooperating, or involving secret cooperation, in order to do something illegal or underhanded.
conniving adjective acting together in secret toward a fraudulent or illegal end
involving collusion; fraudulently contrived by agreement: a collusive agreement to increase prices.