How secure are the decentralized nodes?

I colloquially understand the inherent security provided by the decentralized distribution of the nodes that host the Bitcoin network. However, is the distribution of the devices which run the nodes known? More specifically, are these devices secure? Is it possible the majority of the machines which host the nodes, geographically distributed as they are, are unprotected against sophisticated hacks from malevolent actors? (Ie random old computers with outdated firewalls)? Could a nation state corrupt the nodes?
Additionally, what is the impact of node corruption specifically?