McAfee AVDCDE-BA-CA User Guide - Page 9
Viruses and the PC revolution, Boot-sector viruses - early
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Preface Some of these students soon discovered that they could use certain features of the host computer's operating system to give them unauthorized access to computer resources. Others took advantage of users who had relatively little computer knowledge to substitute their own programs-written for their own purposes-in place of common or innocuous utilities. These unsophisticated users would run what they thought was their usual software only to find their files erased, to have their account passwords stolen, or to suffer other unpleasant consequences. Such "Trojan horse" programs or "Trojans," so dubbed for their metaphorical resemblance to the ancient Greek gift to the city of Troy, remain a significant, and growing, threat to computer users today. Viruses and the PC revolution What we now think of as true computer viruses first appeared, according to Robert Slade, soon after the first personal computers reached the mass market in the early 1980s. Other researchers date the advent of virus programs to 1986, with the appearance of the "Brain" virus. Whichever date has the better claim, the link between the virus threat and the personal computer is not coincidental. The new mass distribution of computers meant that viruses could spread to many more hosts than before, when a comparatively few, closely guarded mainframe systems dominated the computing world from their bastions in large corporations and universities. Nor did the individual users who bought PCs have much use for the sophisticated security measures needed to protect sensitive data in those environments. As further catalyst, virus writers found it relatively easy to exploit some PC technologies to serve their own ends. Boot-sector viruses Early PCs, for example, "booted" or loaded their operating systems from floppy disks. The authors of the Brain virus discovered that they could substitute their own program for the executable code present on the boot sector of every floppy disk formatted with Microsoft's MS-DOS, whether or not it included system files. Users thereby loaded the virus into memory every time they started their computers with any formatted disk in their floppy drives. Once in memory, a virus can copy itself to boot sectors on other floppy or hard disks. Those who unintentionally loaded Brain from an infected floppy found themselves reading an ersatz "advertisement" for a computer consulting company in Pakistan. With that advertisement, Brain pioneered another characteristic feature of modern viruses: the payload. The payload is the prank or malicious behavior that, if triggered, causes effects that range from annoying messages to data destruction. It's the virus characteristic that draws the most attention-many virus authors now write their viruses specifically to deliver their payloads to as many computers as possible. User's Guide ix