Which of the following is the BEST course of action when an online company discovers...

The BEST course of action when an online company discovers a network attack in progress is to isolate the affected network segment. This prevents the attacker from gaining further access to the network and limits the scope of the attack. Dumping event logs to removable media and enabling trace logging may be useful for forensic purposes, but should not be the first course of action in the midst of an active attack. Shutting off all network access points would be too drastic and would prevent legitimate traffic from accessing the network.