Summary: Security is becoming a major concern in Multiagent Systems (MAS), since an agent’s incorrect or inappropriate behaviour may cause non-desired effects such as money and data loss. Moreover, the lack of security in some current MAS-based applications is one of the reasons why MAS technology is being slowly introduced into industry. However, adding security features such as authentication, integrity and confidentiality results in a performance penalty. In this paper, a security infrastructure for a Multiagent Platform (MAP) is presented. It is based on both the Kerberos protocol and the Linux Operating System access control. The design of this infrastructure is focused not only on security but also on efficiency so that the MAP being secured allows the development of secure and efficient Multiagent Systems.