Facts and Questions

How does a virus spread?

The way a virus spreads to other computers varies with the type of virus.
A macro virus becomes active when a document infected with the virus is opened using the program it is designed to attack. (So far--as of October 1997--only Microsoft Word, Microsoft Excel, and Lotus Ami Pro are vulnerable to macro viruses.) The program must have its ability to run macros enabled (turned on). Generally, when a virus in a document becomes active, it will spread to global settings for the application, so that other documents will become infected when they are opened. When an infected document is opened on another computer, the global settings used by that copy of the application will be infected as well.
A boot sector virus infects hard disks and diskettes. If a computer is re-booted or its power is turned on while an infected diskette is in drive A, the virus will spread to the hard disk, even if the diskette is not capable of starting up the computer. Once the hard disk is infected, all diskettes used in the computer will be infected and can spread the infection to other computers. On Macintoshes, a boot sector virus can become active when an infected diskette is inserted in a diskette drive because the Macintosh reads the diskette immediately.
A program virus becomes active when a program infected with a virus is run. Once a program virus is active, it will usually infect other programs on the computer. If a copy of an infected program is moved to and run on another computer, it can then infect programs on that computer.

Can a virus spread through e-mail?

It is possible to get a virus through e-mail but only in very limited circumstances. If you are using an e-mail program that can handle files attached to an e-mail message, you may be vulnerable. To get an infection, the attachment must carry an infection and the e-mail program must be set to do something automatically when it sees the attachment. If the attatchment is a program, the e-mail program would have to run the program without asking you; if the attachment is a document, the e-mail program would have to run a program to open that document. In the latter case (opening a document), the program would have to be configured to allow running macros. If any of the above circumstances are not true for you, you're in no danger of being infected by a virus when you read e-mail. If you save the attachment from an e-mail message, and it is a program or a file that might contain a macro virus, you should scan it with an anti-virus program before opening it.

How can one get rid of a virus?

Generally, you need an anti-virus program to remove a virus from your computer. The University of Delaware provides anti-virus software for PC's running DOS or Windows and for Apple Macintosh computers.
Most anti-virus software requires that no virus is active when the software runs. To start an IBM-compatible computer without activating a virus, you must boot the computer from a diskette that is not infected with a virus. After the computer is operating, anti-virus software can check for viruses, and in most cases, remove them.
Apple Macintosh computers can be checked for viruses after starting the computer normally (without using a diskette).
After you have removed viruses from a hard disk and files, you may want to check your diskettes for viruses as well. Start your computer normally, booting from the (now disinfected) hard disk. If you do not have anti-virus software installed on the hard disk, do so. Then, run the software from the hard disk and have it check your diskettes, one by one, for viruses.
What is a bootable diskette?
A bootable diskette is one that can be used to start a computer without making any use of the computer's hard disk. Such a diskette is a useful tool when combating viruses because it allows one to start (boot) the computer knowing that a virus will not become active.

From a DOS prompt, the command
FORMAT A:/S

Will create a bootable diskette. This command must be issued on a computer known not to be infected with any viruses; otherwise, the bootable diskette may be infected, making it useless as a tool to combat viruses.
Some computers make use of special software to compress the information on the hard disk. This software must be included on the diskette used to boot such computers to make the hard disk readable. If compression software included with a particular version of MS-DOS is being used, that version of MS-DOS will automatically install the necessary compression software on the diskette when it is formatted using the command listed above. If commercial compression software is used on a computer's hard disk, that software should be included on any diskette used to boot that computer.

How can I keep my computer free from viruses?

A common component of anti-virus software is a "resident" program that checks files and disks for virus infections before letting you use them. (A "resident" program runs when you start your computer, and it continues to run "behind the scenes" while you use the computer.) If it finds something that seems to be infected, it will warn you and probably will not let you continue whatever you were doing until you fix the problem. You may need to run a separate program to remove the virus from the infected file(s) or disk(s).

Is a resident program all I need for virus protection?

Some vendors' resident programs are less powerful than their program for performing a full scan for viruses. This is usually done to keep the resident program from slowing your computer's performance. Also, there are ways a virus can get past a resident anti-virus program. For instance, if you start a computer running MS-DOS or Windows from an infected diskette, the virus will spread to your hard disk.
For the above reasons, you should not rely solely on a resident program to protect your computer from viruses, but you should use a scanning program on a regular basis to check for viruses. If you (or others who use your computer) frequently get files and diskettes from others, you may want to scan daily or weekly. If you never share files or diskettes with others, you may only need to scan every few months.