GEN:SID 1:1689
Message ORACLE sys.all_users access
Summary This event is generated when a command is issued to an Oracle database server that may result in a serious compromise of the data stored on that system.
Impact Serious. An attacker may have gained superuser access to the system.
Detailed Information This event is generated when an attacker issues a special command to an Oracle database that may result in a serious compromise of all data stored on that system.

Such commands may be used to gain access to a system with the privileges of an administrator, delete data, add data, add users, delete users, return sensitive information or gain intelligence on the server software for further system compromise.

This connection can either be a legitimate telnet connection or the result of spawning a remote shell as a consequence of a successful network exploit.

Oracle servers running on a Windows platform may listen on any arbitrary
port. Change the $ORACLE_PORTS variable in snort.conf to "any" if this
is applicable to the protected network.
Affected Systems  
Attack Scenarios Simple. These are Oracle database commands.
Ease of Attack Simple.
Corrective Action Use a firewall to disallow direct access to the Oracle database from sources external to the protected network.
Ensure that this event was not generated by a legitimate session then investigate the server for signs of compromise

Look for other events generated by the same IP addresses.
Additional References