A method and system is described for selectively downloading antidotes onto a client computer. The client computer is connected via a network interface card (NIC) to a network that contains an anti-virus server. The NIC is initially logically isolated from the client computer, thus permitting the NIC to autonomously examine packets to and from the client computer and the network. The NIC selectively accepts packets only from trusted Internet Protocol (IP) addresses that conform to a security format such as Internet Protocol Security (IPSec).