HIGHLY destructive nanobot, or doombug for want of a better name, likely too small to see without magnification, could yet be complex enough that it surely would never have been constructed by chance in nature, nor have evolved via other generally lesser forms, like a present-day virus or germ.
Thus there would most likely be no natural defenses in place against such a bug, accrued during the billions of years of evolutionary acclimation to time-honored hazards: viruses, bacteria, all of their possible mutations, etc.
(Chemists have yet to create life from scratch in the lab, so must be complex to start with.)
A doombug could accidently escape or be released from a secret laboratory, or deliberately, via a madman. It could be hacked at home by a demented genius, young or old, and used to blackmail the entire human race. It could be an act of world suicide imposed by an insane cult leader.
The greatest hope, albeit slight, is that such a bug would be a physical impossibility. But the much greater likelihood is that not only is a doombug possible, but the number of potential designs is countless. Then the hope is that the threat can be properly and successfully defended against.
Let’s briefly look at possible defenses:
While it would be impractical if not impossible to keep the tremendously powerful computers capable of aiding in designing a doombug out of the hands of individuals, it is conceivable that the nanoassemblers, the machines necessary for a bug’s actual fabrication, could be so secured.
However we shouldn’t count on this, since these machines would be so useful to every aspect of life, from medication to education— not to mention pest extermination and recreation— that control of their proliferation may be out of the question.
The next possible defense would be some kind of antibug. (The future isn’t Star Wars, it’s Bug Wars.) These could come in either of two basic types, active and reserve (go to the phone, and have your credit card handy):
(1) Active antibugs, carefully tested for safety and lack of mutative ability even under every conceivable stressor, could be pre-released. Acting as sentinels, they’d look out for doombugs, registering an alert.
They might have a built-in capability, like white blood cells in the human body, to knock-out doombugs in the body we call Earth, possibly even being able to multiply quickly in troubled areas at a moment’s notice and then dissipating once the threat is removed.
(2) Reserve antibugs would not have to be so carefully feared, since they would be kept in storage until needed. In the event of an attack, only the variety or varieties necessary to combat the particular doombug would be released.
This kind of antibug could also be designed so as to be quickly and easily modifiable to best combat the particular doombug detected.
In order for antibugs to be available in time, research would have to be conducted into possible doombugs. This in itself is a risk, because it would be necessary to at least design possible doombugs, if not actually build them, for testing purposes.
Perhaps though it would be sufficient to perform actual testing only on relatively harmless bugs, leaving the nastiest ones for computer modeling only.