A cooperative non-orthogonal multiple access (NOMA) communication is a promising solution to improve both the reliability and the capacity of the NOMA system. However, a relay can be exploited by a cooperative attack, this leads to a degradation of performance and secure of the NOMA system. Therefore, we propose a proactive protection scheme to mitigate the effect of the cooperative attack on the NOMA system. We consider the secrecy outage probability (SOP) of the cooperative NOMA in two cases: (1) the NOMA system has no protected scheme; (2) the NOMA system implements the protected scheme using the proactive attack technique. The results demonstrate that using proposed proactive attack scheme improve the secrecy performance of the system. Monte-clalo simulations are provided to examine our proposed scheme.