Cloud computing has become nowadays a buzzword among IT and industry engineers. The cloud phenomenon is quickly growing towards becoming the de facto standard of computing, storage and hosting, both in industry and Internet. This paper presents analysis of security issues inside enterprise private clouds. The investigated security tools were: security groups, elastic IPs, virtual machines isolation. All these mechanisms and tests presented in the paper base on Eucalyptus cloud structure and give a detailed view on process of securing the resources inside private IaaS cloud structure.