Computer programming has for decades posed several difficulties for students of all educational levels. A number of teaching approaches have been proposed over the years but none seems to fulfil the needs of students nowadays. Students use computers mainly for playing games and the Internet and as quite a few researchers state this aspect of computers should be taken into account in the way we educate them. Towards this direction, this paper aims to examine the effects of using an educational Massive Multiplayer Online Role Playing Game (MMORPG) on teaching and learning computer programming. The educational features of an MMORPG called CMX are presented along with a design framework that was devised taking into account previous work in designing educational games. The effects of CMX on teaching and learning computer programming are assessed through a study with first-year undergraduate students. Seventy six students used CMX over a period of five weeks for learning various procedural programming concepts. Students evaluated various aspects ofCMX by filling in a questionnaire that was based on an evaluation framework, which was devised in accordance with the design framework of CMX. Moreover, the results of a midterm exam that took place prior to using CMX and students' accomplishments in the context of CMX were recorded and analyzed. The results show that the majority of the students was entertained by playing the game while learning, and felt motivated to continue based on the game's scenario due to the variety of activities included. In regards to the students' performance, a pre-test and a post-test were carried out in the experimental group, i.e., the participants of this study, and the control group, i.e., students of the course that continued to get taught the same concepts and performed the same assignments as the experimental group, but traditionally. The pre-test and post-test analysis of the performance results for both groups showed that the majority of the students in the experimental group increased their performance in computer programming. Furthermore, students stated they had a positive attitude in regards to re-using CMX in the future in order to learn additional programming concepts. The positive results of this study pave the way for CMX being used in the classroom and expanding the game's functionalities that will further increase students' performance and support teachers in delivering the required knowledge. Moreover, the work reported in this paper offers game designers and teachers methodological and empirical results for game-based learning in such a difficult domain as is computer programming. What is more, the design and evaluation frameworks presented are general enough that they can be easily adjusted and/or extended for designing and assessing educational games in other domains as well.