Computer virus-antivirus coevolution

Virus writers have programmed more than 10,000 DOS-based computer viruses, as of November 1997. As antivirus products improve and detect the latest and greatest viruses, the virus authors invent new and more devious ways to hide their progeny. This coevolution has led to the creation of the most complex class of virus to date: the polymorphic computer virus. These cunning viruses simply cannot be detected cost effectively using traditional antivirus scanning algorithms. Fortunately, the antivirus producers have responded, as they have in the past, with an equally creative solution to the polymorphic virus threat. Many antivirus programs are now starting to employ a technique known as generic decryption to detect even the most complex polymorphic viruses quickly and cost effectively. A computer virus is a self-replicating computer program that spreads by attaching itself to executable files or system areas on diskettes. Recently, programmers have also encountered a new type of virus that infects application data files that contain macros. These viruses are constructed entirely of application macros and use the macro language to propagate themselves