Malwares have been being a major security threats to enterprises, government organizations and end-users. Beside traditional malwares, such as viruses, worms and trojans, new types of malwares, such as botnets, ransomwares, IoT malwares and crypto-jackings are released daily. To cope with malware threats, several measures for monitoring, detecting and preventing malwares have been developed and deployed in practice, such as signature-based detection, static and dynamic file analysis. This paper proposes 2 malware detection models based on statistics and machine learning using opcode n-grams. The proposed models aim at achieving high detection accuracy as well as reducing the amount of time for training and detection. Experimental results show that our proposed models give better performance measures than previous proposals. Specifically, the proposed statistics-based model is very fast and it achieves a high detection accuracy of 92.75\% and the random forest-based model produces the highest detection accuracy of 96.29\%.