The purpose of this study was to examine what security issues exist in cloud storage services. We examine the solutions offered by Google Drive, Dropbox and OneDrive and make a comparison among these three services from a security perspective. Cloud storage is one of the cloud computing services that has become popular in recent years because of the spreading of smartphones and tablets. According to previous theo-ries, there are many security issues affecting cloud storage. In this study we examined Google Drive, Dropbox and OneDrive from a security perspective. We did a compari-son between the solutions offered by these three providers.Our criteria were taken from the cloud security alliance that has a list over the most im-portant security issues affecting cloud computing. We took information about the secu-rity solutions from the providers' white papers and support sites.Our results show that the three providers have similar security procedures and that they use many security technologies like TLS, two factor authentication and defense in depth. Results also show that each one of them has a superior procedure in a particular area compared to the others, and that made it difficult to decide which one is the best.