Cloud computing is revolutionizing the way that companies use IT services. The advantages of cloud computing for companies are numerous, from substantial cost reductions to global access to data. However, this new channel of communication brings a new antitrust risk, exchange of sensitive information among competitors in the cloud. The features of cloud computing (i.e., data location) together with some IT techniques (i.e., encryption of information) may facilitate the creation of sophisticated systems to share information illegally. These new systems may even prevent antitrust authorities from finding evidence of the illicit conduct. This article shows how companies engaged in cartel activities may remain undetected by competition authorities if they use sophisticated techniques. This article further discusses the tools available to competition authorities to detect and to prevent this behaviour, arguing that some authorities are a priori better prepared than others to combat these 'cloud cartels'. The final section of this article suggests new policies to deter the illegal use of cloud computing services.