GB2231418A - Computer viruses - Google Patents

Abstract

In order to maintain a computer/hard disk system free from boot sector and partition record viruses, a hardware device is added to the computer that prevents writing to cylinder zero of the hard disk, and a method is provided for setting up the disk so that the boot sector and partition record are within the write-protected area, and all other parts of the disk are write enabled. <IMAGE>

Description

COMPUTER VIRUS PREVENTER This invention relates to computer systems, and in particular with the problems caused by computer viruses.

An additional claim is made for a method for preventing unauthorised personnel from writing anything at all to any part of the hard disk.

Computer viruses spread from one system to another, and as well as replicating themselves can contain additional code to do whatever the programmer intends, which could be anything from a harmless prank, to a destructive act.

This invention relates to Boot sector and Partition record viruses, so called because they reside in the important sector of a disk containing code that is used when a computer is started up.

These kinds of viruses can take control of the computer before any other software is run, and can therefore hide themselves from subsequent programs.

In order to prevent infection of the boot sector or partition record, this invention provides a way to prevent writes to the very first cylinder of the hard disk, which is where the partition record and the boot sector both reside. This is done by means of a small electronic circuit, which detects when the drive is at the first cylinder, and disables writing to the disk in that circumstance. Thus, the hard disk cannot be infected.

The method used is to detect the "Track 00" line (normally line number 10) and when this line indicated that the read/write heads are over cylinder zero (also known as track zero), the "write gate" line (normally line 6) is modified to inhibit writing to the drive.

In order to initialise the disk, this first cylinder must be written to, so provision is made to disable this circuit, using a switch or jumper. A third component of the system is a program that moves the boot sector of the disk to a position just inside the protected area, but with the rest of the disk (which must be write enabled) outside the protected area. This program may also replace the partition or boot sector programs, as some of these do not have the full specified functions, but only a subset.

Figure 1 is a map of the hard disk, as it is normally set up. The first cylinder is used for the Partition and the Boot sector, but also for the FAT area of the disk, which must be write enabled in normal use.

Figure 2 is a map of the hard disk as set up with the software that is used in this invention. Notice that the sectors to be protected are on cylinder zero, the first cylinder, and all other sectors are outside cylinder zero.

Figure 3 shows an implementation of the invention, and shows how it stands as a gatekeeper between the hard disk and the controller. There are two switches on the circuit boar#d; one of these disables writes to cylinder zero, and the other disables all writes.

The invention operates by detecting when the hard disk read/write heads are on cylinder zero, using the recalibration line. When this is the case, an electronic circuit disconnects the line that enables writing to the disk. The software ensures that the partition record, and the boot sector, are on cylinder zero, but that all the areas that must be writable, are outside.

This system will operate with various operating systems, using different set up software for different operating systems.

Claims (4)

CLAIMS:

1. A method of operating a hard disk computer system, wherein virus-free code is protected on the partition record and boot sector by disabling writes to that part of the disk using hardware methods to disable the write line.

2. A method for setting up the disk so that the partition record and boot sector is inside the write protected area, and the rest of the disk is outside it.

3. A computer/disk system having a device fitted as in claim 1, and set up using method 2.

4. A computer/disk system, method of operation thereof, or memory device, substantially as described with reference to the drawings and the descriptions.