A honeynet is a research tool consisting of a network specifically designed for the purpose of being compromised, with control mechanisms that prevent this network from being used as a base for launching attacks against other networks. Once compromised, the honeynet can be used to observe the intruders' activities, collect tools and determine new trends in network attacks. In this paper we discuss the implementation of a honeynet, based entirely on open source software, that meet the requirements listed above. We present its topology, the tools developed and the results achieved. We also discuss how valuable a honeynet can be to better understand the threats to the constituency of a Computer Security Incident Response Team (CSIRT).