We already do. Take for example the basic virus scanner. The whole anti-bodies system works very similar to hash scan method currently used today. Until adware

We already do. Take for example the basic virus scanner. The whole anti-bodies system works very similar to hash scan method currently used today. Until adware/virus/worm gets marked by a hash (from the providers database) the scanner really doesn't care. The major failing of this system is unlike the real world (or possibly like the world with the advent of genetic research) you have a lot of very smart people continually attempting to defeat the status quo system. Nature luckily, doesn't have the malice or know-to as a much of dedicated hackers.