SNMP is a standard protocol used to monitor or manage a system. SNMPv1/v2c provides no encryption and uses community strings as a form of authentication. Community strings are sent in cleartext over the network and are usually shared across a group of individuals, rather than being private to an individual user. SNMPv3, on the other hand, uses encryption to provide a secure channel and has individual user names and passwords. SNMPv3 user passwords are localized so that they can be stored securely on management stations.
Oracle recommends that SNMPv3 be used if supported by the native SNMP agent. See the documentation for net-snmp or the Windows SNMP service for instructions on how to configure SNMPv3.