Simple Network Management Protocol (SNMP) is a protocol which can be used by administrators to remotely manage a computer or network device. There are typically 2 modes of remote SNMP monitoring. These modes are roughly 'READ' and 'WRITE' (or PUBLIC and PRIVATE).
If an attacker is able to guess a PUBLIC community string, they would be able to read SNMP data (depending on which MIBs are installed) from the remote device. This information might include system time, IP addresses, interfaces, processes running, etc. If an attacker is able to guess a PRIVATE community string (WRITE or 'writeall' access), they will have the ability to change information on the remote machine. This could be a huge security hole, enabling remote attackers to wreak complete havoc such as routing network traffic, initiating processes, etc. In essence, 'writeall' access will give the remote attacker full administrative rights over the remote machine. Note that this test only gathers information and does not attempt to write to the remote device. Thus it is not possible to determine automatically whether the reported community is public or private. Also note that information made available through a guessable community string might or might not contain sensitive data. Please review the information available through the reported community string to determine the impact of this disclosure.
Determine if the detected community string is a private community string. Determine whether a public community string exposes sensitive information. Disable the SNMP service if you don't use it or change the default community string.