Phage, Vermes & Equine

Phage, Vermes &Equine
Computer users want to know how to protect themselves from computer viruses.

Sometimes protecting a client's computer is as simple as helping them install a solid antivirus program; however, others will want to know why some are called viruses, others worms or Trojan horses.

Which is it?

Many malicious programs can be classified as all three: virus, worm, and Trojan horse. For example, the original Melissa virus infects files (making it a virus), but also uses email to spread itself to other computers (making it a worm) and appears to be a list of adult sites (making it a Trojan horse).

Here's a quick description of the three classifications. (The Latin names are contrived for humor.)

Virus (filia infectus)

A virus is a program that spreads itself by infecting files. When the infected file is opened, the virus runs its code first, and then it may open the intended file, as initially requested.

Viruses usually spread only when an infected file is transferred from one computer to another. Such as an email attachment, across a local area network, downloaded from the Internet, or through sneakernet (sharing of floppy diskettes).

Worm, email (Lumbricus mailus)

Worms don't infect files, but entire disks or computer systems.

Worms generally require user intervention before they can be transferred to another system. The most common way today is via email attachment.

Worms such as AnnaKournikova, spread after an email attachment is executed. Common PC worms use Microsoft's ActiveX programming language to spread to all addressees in the attacked user's email address book.

Worm, network (Lumbricus netus)

Some worms are able to exploit security holes in networked computers and gain entry to the system.

Internet and intranet-connected computers running unpatched DNS (Domain Name Server) and FTP (File Transfer Protocol) applications are common targets for worms.

Email-borne worms can be stopped dead if the attachment isn't executed. Keeping email software updated, especially Microsoft Outlook, which can automatically execute ActiveX commands, and deleting unknown file attachments are two steps that all users should take.

Trojan horse (Equus trojanus)

A Trojan horse wants to be executed.

Strictly speaking, a Trojan horse is any program that does something other than what is expected; however, this describes just about all software applications :-).

Trojan horses often open back doors to network systems to grant entry to a worm. Even stand-alone systems, including home PCs, are susceptible to attacks from Trojan horses.

What do those words mean?

Phage: a program that modifies programs or files in unauthorized ways; especially one that propagates a virus or Trojan horse.
Vermes: an extensive, artificial division of the animal kingdom, including the parasitic worms, or helminths, together with the nemerteans, annelids, and allied groups.
Equine: of, pertaining to, or resembling, a horse

Where to go from here

If you'd like more information about viruses, worms, and Trojan horses, I suggest you visit Damar Group's antivirus page. It has links to useful, free antivirus resources.

Dave Murphy is a computer trainer located in Howard County. He owns Damar Group, an IT services firm, and he founded the professional society for computer trainers, now with members in 158 countries. You'll reach him at 410.567.5366.

updated June 15, 2001
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