What Wireshark is not
Wireshark is not an intrusion-detection system. It will not warn you when people do strange things on your network that they are not allowed to do. However, if strange things happen, Wireshark might help you figure out what really is going on. It is like a monitoring device.
Wireshark will not manipulate things on the network; it will only measure things from it. It does not send packets on the network or do other active things.