VIRUS FAQ
General Virus Information | Viruses: The Threat is Real | Types of Viruses | Macintosh Viruses
A virus is a piece of software designed and written to adversely affect your computer by altering the way it works without your knowledge or permission. In more technical terms, a virus is a segment of program code that implants itself to one of your executable files and spreads systematically from one file to another. Computer viruses do not spontaneously generate: They must be written and have a specific purpose. Usually a virus has two distinct functions:
A benign virus is one that is designed to do no real damage to your computer. For example, a virus that conceals itself until some predetermined date or time and then does nothing more than display some sort of message is considered benign.
A malignant virus is one that attempts to inflict malicious damage to your computer, although the damage may not be intentional. There are a significant number of viruses that cause damage due to poor programming and outright bugs in the viral code. A malicious virus might alter one or more of your programs so that it does not work as it should. The infected program might terminate abnormally, write incorrect information into your documents. Or, the virus might alter the directory information on one of your system area. This might prevent the partition from mounting, or you might not be able to launch one or more programs, or programs might not be able to locate the documents you want to open.
Some of the viruses identified are benign; however, a high percentage of them are very
malignant. Some of the more malignant viruses will erase your entire hard disk, or delete
files.
It is not overstating the case to say that viruses could interrupt the free flow of information that has been built up by the personal computing in the last 10 years. Indeed, the prevalence of viruses has ushered in a new era of safe computer to the point where those that ignore the guidelines run grave risks. Considering the extreme warnings of danger--and the incidents already on record--it is a mystery that there are those in the computing industry who claim news reports of viruses are exaggerated.
The National Center for Computer Crime Data in Los Angeles estimates that American business have lost as much as $550 million from unauthorized access to computers yearly. The amount of lost time may be incalculable.
As an indication of the severity of the problem, the federal government has helped to form a virus SWAT team called the Computer Emergency Response Team. Its job is to investigate security threats in major computer networks across the country. The Software Publishers Association has also adopted certain measures to address the problem.
Furthermore, in the last year many Fortune-listed companies have begun to establish computer policies to deal with viruses. In many cases those new procedures will set practices for testing in all software before it is put on a network and restrict the downloading of software from electronic bulletin boards. Literally no one who uses computers--not the government nor the police nor even your local bank--is immune from computer viruses.
Suppose a space shuttle executed order from a virus-infected software program. Or an air traffic controller was given incorrect information from a fouled system. Or your company's financial records were suddenly eradicated or permanently altered.
These are not necessarily fantasies of impending doom. Thus far, computer viruses have
hit a variety of systems, including Fortune 500 companies, government agencies, major
universities, newspapers and large networks linking vast numbers of computers and huge
volumes of information.
A computer virus is a program designed to replicate and spread on its own, preferably without you known it exists. Computer viruses spread by attaching themselves to another program (such as your word processing or spreadsheet programs) or to the boot sector of a diskette. When an infected file is executed, or the computer is started from an infected disk, the virus itself is executed. Often, it lurks in memory, waiting to infect the next program that is run, or the next disk that is accessed. In addition, many viruses also perform a trigger event, such as displaying a message on a certain date, or deleting files after the infected program is run a certain number of times. While some of these trigger events are benign (such as those that display messages), other can be detrimental. The majority of viruses are harmless, displaying messages or pictures, or doing nothing at all. Other viruses are annoying, slowing down system performance, or causing minor changes to the screen display of your computer. Some viruses, however, are truly menacing, causing system crashes, damaged files and lost data.
These are viruses that attach themselves to (or replace) .COM and .EXE files, although in some cases they can infect files with extensions .SYS, .DRV, .BIN, .OVL and .OVY. With this type of virus, uninfected programs usually become infected when they are executed with the virus in memory. In other cases they are infected when they are opened (such as using the DOS DIR command) or the virus simply infects all of the files in the directory it was run from (a direct infector).
Every logical drive, both hard disk and floppy, contains a boot sector. This is true even of disks that are not bootable. This boot sector contains specific information relating to the formatting of the disk, the data stored there and also contains a small program called the boot program (which loads the DOS system files). The boot program displays the familiar "Non-system Disk or Disk Error" message if the DOS system files are not present. It is also the program that gets infected by viruses. You get a boot sector virus by leaving an infected diskette in a drive and rebooting the machine. When the boot sector program is read and executed, the virus goes into memory and infects your hard drive. Remember, because every disk has a boot sector, it is possible (and common) to infect a machine from a data disk. NOTE: Both floppy diskettes and hard drives contain boot sectors.
The first physical sector of every hard disk (Side Ø, Track Ø, Sector 1) contains the disk's Master Boot Record and Partition Table. The Master Boot Record has a small program within it called the Master Boot Program which looks up the values in the partition table for the starting location of the bootable partition, and then tells the system to go there and execute any code it finds. Assuming your disk is set up properly, what it finds in that location (Side 1, Track Ø, Sector 1) is a valid boot sector. On floppy disks, these same viruses infect the boot sectors.
You get a Master Boot Record virus in exactly the same manner you get a boot sector virus -- by leaving an infected diskette in a drive and rebooting the machine. When the boot sector program is read and executed, the virus goes into memory and infects the MBR of your hard drive. Again, because every disk has a boot sector, it is possible (and common) to infect a machine from a data disk.
Multi-partite viruses are a combination of the viruses listed above. They will infect both files and MBRs or both files and boot sectors. These types of viruses are currently rare, but the number of cases is growing steadily.
Some viruses are programmed specifically to damage the data on your computer by corrupting programs, deleting files, or erasing your entire hard disk. Many of the currently known Macintosh viruses are not designed to do any damage. However, because of bugs (programming errors) within the virus, an infected system may behave erratically.
Computer viruses don't infect files on write-protected disks and don't infect documents, except in the case of Word macro viruses, which infect only documents and templates written in Word 6.0 or higher. They don't infect compressed files either. However, applications within a compressed file could have been infected before they were compressed. Viruses also don't infect computer hardware, such as monitors or computer chips; they only infect software.
In addition, Macintosh viruses don't infect DOS-based computer software and vice versa. For example, the infamous Michelangelo virus does not infect Macintosh applications. Again, an exception to this rule are the Word and Excel macro viruses, which infect spreadsheets, documents and templates which can be opened by either Windows or Macintosh computers.
Finally, viruses don't necessarily let you know that they are there - even after they do something destructive.
Viruses spread when you launch an infected application or start up your computer from a disk that has infected system files. For example, if a word processing program contains a virus, the virus activates when you run the program. Once a virus is in memory, it usually infects any application you run, including network applications (if you have write access to network folders or disks).
Viruses behave in different ways. Some viruses stay active in memory until you turn off your computer. Other viruses stay active only as long as the infected applications is running. Turning off your computer or exiting the application removes the virus from memory, but does not remove the virus from the infected file or disk. That is, if the virus resides in a system file, the virus will activate the next time you start your computer from the infected disk. If the virus resides in an application, the virus will activate again the next time you run the application.
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Copyright © 1999 Keith Nolan. Click here for legal information.