On Windows machines, SNMP is run through the 'SNMP' service. To change the community string:
- Open Control Panel -> Administrative Tools -> Services
- Find 'SNMP Service', right click it, and choose Properties
- On the Security tab, click the 'Add' button near 'Accepted community names'
- Enter a secure password for this (do not reuse any existing password)
- Make sure to remove any insecure passwords (default values such as 'public' or 'private' are commonly abused)
- Click OK
- Restart the SNMP service
On Linux machines, SNMP is commonly run through the net-snmp library:
- Open your snmpd.conf file (usually /etc/snmp/snmpd.conf)
- Find the line that looks like: 'com2sec notConfigUser default public' (the line will begin with com2sec and end with a password. In this example, the password is 'public')
- Change the 'public' at the end of the line to a more secure password
- Restart the SNMP server with: 'service snmpd restart'