In August 2008, the Polish Competition and Consumer Protection Authority (CCPA) referred to the European Commission the results of its proceedings concerning the conditions of sale of laptops with a pre-installed Windows operating system. According to the CCPA, Microsoft and laptop manufacturers might have entered into an agreement prohibited under Article 81 of the EC Treaty. This paper claims that the effects of the Microsoft‘s practice may go beyond the computer software market. Yet, enforcement of competition law in the sectors of new economy is a complex task due to the high risk of false positive and false negative errors, both of them resulting in efficiency loss. The overall aim of the paper is to stress that in order to be an effective tool for the regulation of competition, antitrust analysis should go deep into the understanding of the economic consequences of the practice involved.