What I don't understand is why someone doesn't finally write a piece of malware that destroys botnets? These unmaintained machines cause the entire world so much grief.
It doesn't have to be mean and destroy data, just incapacitate the machines and force the users to upgrade.
Existing botnet malware already protects itself against removal or interference from other malware and anti-virus software. And it usually has auto-update functionality. It would just be extended to defend against this new "anti-malware" as well.
Besides, if this hypothetical "anti-malware" actually incapacitated machines, it would be highly illegal itself.
It doesn't have to be mean and destroy data, just incapacitate the machines and force the users to upgrade.