A method of managing suspicious devices on a network, the method comprising: if a device to be managed and having a certain abnormal management item is referred to as a suspicious device and the certain abnormal management item is referred to as a suspicious management item, setting based on a manager's input or selection a suspicious group, the suspicious group including subgroups corresponding to each of at least one suspicious management item which is a criteria used for determining whether the device is the suspicious device for managing a plurality of devices on a network, wherein the setting is performed by a user interface module; accessing the devices and reading information corresponding to the suspicious management item, wherein the accessing and the reading are performed by a device discovery module; determining whether each device is a suspicious device based on the information corresponding to the suspicious management item, and registering the device in a subgroup of the suspicious group that corresponds to the at least one suspicious management item if the device is determined as a suspicious device; characterised in that the method further comprises: checking whether an error of the device included in the suspicious group is resolved, wherein the checking is performed by the group registration/elimination module; and eliminating the device from the suspicious group if the error of the device is resolved, wherein the eliminating is performed by the group registration/elimination module; and wherein the determining and the registering are performed by a group registration/elimination module, and wherein the subgroups include at least one of an invalid serial number group, a negative count group, a wrong collection data group, a no response group, an old version group, and a status change group, wherein the subgroups are generated by the user based on one or more conditions set by the user via the user interface. if a device to be managed and having a certain abnormal management item is referred to as a suspicious device and the certain abnormal management item is referred to as a suspicious management item, setting based on a manager's input or selection a suspicious group, the suspicious group including subgroups corresponding to each of at least one suspicious management item which is a criteria used for determining whether the device is the suspicious device for managing a plurality of devices on a network, wherein the setting is performed by a user interface module; accessing the devices and reading information corresponding to the suspicious management item, wherein the accessing and the reading are performed by a device discovery module; determining whether each device is a suspicious device based on the information corresponding to the suspicious management item, and registering the device in a subgroup of the suspicious group that corresponds to the at least one suspicious management item if the device is determined as a suspicious device; characterised in that the method further comprises: checking whether an error of the device included in the suspicious group is resolved, wherein the checking is performed by the group registration/elimination module; and eliminating the device from the suspicious group if the error of the device is resolved, wherein the eliminating is performed by the group registration/elimination module; and wherein the determining and the registering are performed by a group registration/elimination module, and wherein the subgroups include at least one of an invalid serial number group, a negative count group, a wrong collection data group, a no response group, an old version group, and a status change group, wherein the subgroups are generated by the user based on one or more conditions set by the user via the user interface. checking whether an error of the device included in the suspicious group is resolved, wherein the checking is performed by the group registration/elimination module; and eliminating the device from the suspicious group if the error of the device is resolved, wherein the eliminating is performed by the group registration/elimination module; and wherein the determining and the registering are performed by a group registration/elimination module, and wherein the subgroups include at least one of an invalid serial number group, a negative count group, a wrong collection data group, a no response group, an old version group, and a status change group, wherein the subgroups are generated by the user based on one or more conditions set by the user via the user interface.