The American University in Cairo
School Of Business,Economics And Communication

1. What is a computer virus?

2. What are worms, macro viruses and Trojans?

3. How do viruses spread?

4. What do viruses do to computers?

5. What about viruses in E-mail?

6. Some general tips on avoiding virus infections

7. I think my computer might have a virus; what should I do?



1.  What is a computer virus?

A computer virus is a program designed to spread itself by first infecting executable files or the system areas of hard and floppy disks and then making copies of itself. Viruses usually operate without the knowledge or desire of the computer user.

2.  What are worms, macro viruses and Trojans?

Some people distinguish between general viruses and worms. The "worm" acquired its name because of the way it gradually infects a system, much like a worm eating it' way through an apple. Most worms will try to infect as many computer files as possible, including free space. Other worms duplicate by attaching themselves to e-mail, or other file transfers.
A macro virus is embedded in a document instead of a program. Documents created in programs like Microsoft Word and Microsoft Excel can be infected with macro viruses.
A Trojan Horse is a destructive program that pretends to be a useful one. Most Internet-acquired viruses are initially dropped by Trojans. The Trojan contains the virus code or program, which then infects your computer. So, although the Trojan itself might not be self-replicating, the virus it contains is.

3.  How do viruses spread?

When you execute infected program code, the virus code will run and attempt to infect other programs, either on the same computer or on other computers connected over a network. The newly infected programs will then try to infect yet more programs, and the pattern repeats itself.
When you share a copy of an infected file with other computer users, running the file may also infect their computers; and files from those computers may spread the infection to yet more computers.
If your computer is infected with a boot sector virus, the virus tries to write copies of itself to the system areas of floppy disks and hard disks. Then the infected floppy disks may infect other computers that boot from them, and the virus copy on the hard disk will try to infect still more

4.  What do viruses do to computers?

Viruses are software programs, the actual effect of any particular virus depends on how it was programmed by the person who wrote the virus.
Some viruses are deliberately designed to damage files or otherwise interfere with your computer's operation, while others don't do anything but try to spread themselves around. But even the ones that just spread themselves are harmful, since they damage files and may cause other problems in the process of spreading. Note that viruses can't do any damage to hardware: Warnings about viruses that will physically destroy your computer are usually hoaxes, not legitimate virus warnings.

5.  What about viruses in E-mail?

You can't get a virus just by reading a plain-text E-mail message or Usenet post. What you have to watch out for are encoded messages containing embedded executable code (i.e., JavaScript in an HTML message) or messages that include an executable file attachment (i.e., an encoded program file or a Word document containing macros). In order to activate a virus or Trojan horse program, your computer has to execute some type of code. This could be a program attached to an E-mail, a Word document you downloaded from the Internet, or something received on a floppy disk. There's no special hazard in files attached to Usenet posts or E-mail messages: they're no more dangerous than any other file.

6.  Some general tips on avoiding virus infections:

  1. Install anti-virus software from a well-known, reputable company. Update it regularly, and use it regularly. New viruses come out every single day; an anti virus program that hasn't been updated for several months will not provide much protection against current viruses.

  2. In addition to scanning for viruses on a regular basis, install an 'on access' scanner (included in most good anti-virus software packages) and configure it to start automatically each time you boot your system. This will protect your system by checking for viruses each time your computer accesses an executable file.

  3. Virus scan any new programs or other files that may contain executable code before you run or open them, no matter where they come from.

  4. Anti-virus programs aren't very good at detecting Trojan horse programs, so be extremely careful about opening binary files and Word/Excel documents from unknown or 'dubious' sources. This includes posts in binary newsgroups, downloads from web/ftp sites that aren't well-known or don't have a good reputation, and executable files unexpectedly received as attachments to E-mail or during an on-line chat session.

  5. If your E-mail or news software has the ability to automatically execute JavaScript, Word macros, or other executable code contained in or attached to a message, it strongly recommend that you disable this feature.

  6. Be extremely careful about accepting programs or other files during on-line chat sessions.

  7. Do regular backups. Some viruses and Trojan horse programs will erase or corrupt files on your hard drive and a recent backup may be the only way to recover your data.


7.  I think my computer might have a virus; what should I do?

The safest way to ensure that your computer is virus free is to install a virus scanner with the most recent virus definition files. The ACS has a license for the free installation of Norton anti-virus, and MacAfee for PCs, and Macintosh. The license encompasses a free copy to all faculty, students and staff. For more information visit the ACS site. It is also imperative that you periodically check for updates for the anti-virus programs on their sites, or through the ACS site. In addition the ACS provides technical support, if you are not able to remove the virus. ACS technical support (