Viruses and Windows 95
(Data Fellows)

The soon-to-be-published Microsoft Windows 95 introduces new characteristics to the field of anti-virus activities. Although there have been rumors that the virus threat will be eliminated when Windows 95 comes along, these are, for the most part, insubstantial. In fact, almost all current viruses will be able to function with Windows 95.

Boot sector viruses will be able to infect both hard disk Main Boot Records and the boot sectors of disk partitions quite normally. However, the viruses will not be able to spread to diskettes normally after the initial infection.

When Windows 95 is started, it usually loads a 32-bit disk access system. If, on the other hand, the computer has been infected by a boot sector virus, Windows 95 is shunted to using 16-bit disk access system. In spite of this, some parts of the 32-bit access systems are loaded, and this prevents boot sector viruses from spreading to diskettes. This does not mean that the viruses can be safely left on the disk, however, because they are still able to activate and cause damage. The infection should be removed when it is detected. It should be noted that if the user has set the 16-bit disk access on from the Windows 95 Control Panel, the viruses will be able to spread to diskettes quite normally.

Boot sector viruses that use DOS interrupts to infect diskettes will not be able function under Windows 95 - the operating system's kernel takes command over all DOS interrupts, thus preventing viruses from using them.

Although Microsoft's own anti-virus program will not be supplied with Windows 95, Windows 95 is capable of detecting a boot sector infection by itself. Check the lower half of the Performance page in Control Panel's System program - it may contain a warning about a MS-DOS -compatible disk access state and a possible virus infection. Since this warning is not repeated anywhere else, it is easy for a user to overlook.

File viruses, on the other hand, are able to function under Windows 95 almost as well as under DOS itself. The main difference is that the viruses are only able to spread themselves inside DOS windows opened from Windows 95. This holds true only for the present viruses, however - it is likely that we will soon see viruses written expressly for Windows 95, capable of exploiting its characteristics. Since Windows 95 is technically quite different from earlier versions of Windows, only few currently known Windows viruses will be able to function under it.

Disinfection of Viruses

During installation, Windows 95 asks whether the user wants to create an utility diskette from which the computer can be booted afterwards. It is recommendable to take the program up on its offer, for without such an utility diskette it may prove difficult to disinfect certain boot sector viruses - especially if no anti-virus program is immediately available at the time.

Disinfection of Boot Sector Viruses

In principle, boot sector viruses are disinfected in Windows 95 in quite the same way as in DOS. First, the computer must be booted from a clean diskette - this can be done with either the Windows 95 utility diskette created during installation, or a normal DOS boot diskette. After this, the virus can be disinfected by using an anti-virus program.

If the computer is booted from the Windows 95 utility diskette, the disinfection procedure may in some cases be interrupted by a warning about direct disk access. This warning can usually be disabled by using Windows 95's own LOCK command, but it may sometimes prove necessary to boot the computer from a DOS boot diskette. After a DOS boot, the infection can be disinfected normally with F-PROT for DOS. As can be seen, it is worthwhile to hang onto an old DOS boot diskette even after switching to Windows 95.

If no anti-virus program is immediately available, it is possible to attempt disinfection by using the operating system's own functions. This can be done with the command FDISK/MBR, which can be used both after a DOS- and a Windows 95 diskette boot. However, if the computer's hard disks cannot be accessed normally after a diskette boot, one should not attempt a FDISK/MBR disinfection. In such cases, the infecting virus has probably encrypted the hard disk's partition table - there are viruses that do this, among them the Stoned.Empire.Monkey viruses.

Viruses that have infected the boot sector of a disk partition can be removed manually by using the Windows 95 utility diskette. After the diskette boot, the infection can be removed by simply giving the SYS C: command - this will cause the boot sector and system files to be rewritten on the hard disk. If the computer has been booted from a DOS boot diskette, the SYS C: command should not be used, because it will create a boot sector different from the boot sectors used by Windows 95.

Disinfection of File Viruses

First, the computer should be booted from a clean diskette just to be on the safe side. Windows 95 utility diskettes and DOS boot diskettes are both suitable for booting. After that, the viruses are disinfected just like in DOS.