People are mostly focused on defending the computers on the Internet, and there's been surprisingly little attention to defending the Internet itself as a communications medium. [We] need to pay some more attention to that, because it's actually kind of fragile.

Hillis contrasts endpoint security (protecting individual computers and servers) with the resilience of the network as a whole. The quote argues that treating the Internet merely as a collection of machines overlooks its role as a shared communications substrate with its own vulnerabilities—routing, naming, interconnection, and physical infrastructure. Calling it “fragile” underscores that systemic failures (misconfiguration, cascading outages, attacks on core protocols, or damage to key links) can disrupt communication even if many endpoints are well secured. The remark anticipates later concerns about critical infrastructure protection and the need for defense-in-depth at the network and protocol layers, not just at the device level.