[a1369209993]

> For network communications (IP), practically any two machines can communicate with each other, which opens up a number of serious security risks.

This isn't quite a correct characterization of the problem. The problem - rather in the style of your previous post - is that a given machine will listen to communications from any other machine, and often react to them. My usual go-to example is that most web browsers will happily execute completely arbitrary code from any random website they happen to stumble across.

There are practical reasons (eg opprotunistic scans for exploitable vulnerabilities) to keep machines isolated, but the root problem is not that your machines can send and recieve communications with arbitrary others, but that they choose to.

> How do I find people I like or trust?

I don't have a general solution to this one even in principle, but I've found it helps if you don't need to trust them. Proper anonymity or pseudonymity means I can have a perfectly comfortable conversation even in the depths of 4chan, and laugh in the faces of anyone who tries to threaten me.