32-Bit Operating SystemsOne of the significant environmental changes will be the transition from DOS to 32-bit operating systems for PCs, such as OS/2 and Windows 95. In the next few years, we expect that more and more systems will run 32-bit operating systems in order to better use the increasing power of newer PCs. IBM's OS/2 is a 32-bit operating system that lets users run DOS, Windows and OS/2 programs simultaneously. The effects of computer viruses on OS/2 systems is described elsewhere [17]. Boot viruses do not generally spread from within OS/2 itself, though they can spread from systems that have DOS as well as OS/2 installed in separate partitions. File viruses can often spread to other files when infected programs are run in Virtual DOS Machines (VDM) within OS/2. However, they remain active in the system only as long as the infected VDM is active, which is often only as long as the infected program is running. Some file viruses are likely to not spread in VDMs, simply because of differences between VDMs and DOS. This decreases the rate at which file viruses spread in collections of OS/2 systems [17]. In environments in which OS/2 predominates over DOS, we would expect this to lead to a decline in prevalence of all current DOS viruses. Microsoft's Windows 95 is a 32-bit operating systems that supports DOS, Windows 3.1 and Windows 95 programs. Recent experiments with a pre-release version of Windows 95 suggest that DOS boot viruses will not in general spread well from Windows 95 systems [18]. File viruses were not tested in these experiments. Preliminary experiments carried out at the High Integrity Computing Laboratory with a pre-release version of Windows 95 suggest that some DOS file viruses will spread as usual, some might not, and some might cause system problems. In environments in which Windows 95 predominates over DOS, we would also expect this to lead to a decline in prevalence of all current DOS viruses. Not all of the news is good, however. Viruses can be written for 32-bit operating systems, and the first few such crude viruses have already appeared [17]. These operating systems offer new facilities that viruses can use to both hide and spread. The transition to these newer operating systems will change the virus problem, perhaps significantly, but it will not eliminate it.
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