Cybersecurity is a growing problem, yet a lot of it could be mitigated right now.
Brute force attacks: have a world wide router protocol that shares information from a host that sees itself in danger of overload. The routers can cooperate to lower traffic to that host and possibly identify offending sources.
Bad links: have the client (email, browser, messaging app) look at the text being clicked to see if it matches the link. Have it test the link to see if it redirects elsewhere. Warn the user if there seems to be a mismatch. Further checks could include common misspellings and newly registered domains. These wouldn't catch everything, but they'd stop a lot.
Buffer overflows: Why on earth do these still exist? Because languages that allow it still exist, of course. But is it really not possible to write code that can check other code to see if it allows reads that exceed the stack or buffer? Maybe not 100%, but gosh, some help?
Trojans: I guess we can't ever fix that 100% unless we can fix gullibility and raw stupidity.