John has a proxy server on his network which caches and filters web access. He shuts down all unnecessary ports and services. Additionally, he has installed a firewall (Cisco PIX) that will not allow users to connect to any outbound ports. Jack, a network user has successfully connected to a remote server on port 80 using netcat. He could in turn drop a shell from the remote machine. Assuming an attacker wants to penetrate John’s network, which of the following options is he likely to choose?