Virus vs. Worm – What’s the Difference?

Below you will find information gathered from several resources on the Internet regarding the differences between viruses and worms.

Many computer users believe you can only become infected with a computer bug if you open up an infected e-mail.

Not anymore!

A computer virus is delivered by e-mail messages, according to most definitions.

But a computer worm spreads through the internet.

Viruses are computer programs that are designed to spread themselves from one file to another on a single computer. A virus might rapidly infect every application file on an individual computer, or slowly infect the documents on that computer, but it does not intentionally try to spread itself from that computer to other computers. In most cases, that’s where humans come in. We send email document attachments, trade programs on diskettes, or copy files to file servers. When the next unsuspecting user receives the infected file or disk, they spread the virus to their computer and so on.

Worms, on the other hand, are insidious because they rely less (or not at all) on human behavior in order to spread themselves from one computer to another. The worm is a program that is designed to copy itself from one computer to another over a network (e.g., by use email). The worm spreads itself to many computers over a network, and doesn’t wait for a human being to help. This means that computer worms spread much more rapidly than computer viruses.

“Malware” is the term used to describe any and all malicious software, including viruses, Trojan horse programs, and worms.

Even though "virus" has become a generic term to refer to all types of computer malware, it actually only applies to one specific type of malicious code/file. A computer virus does the same thing a biological virus does, for the most part. It infects a “host” (a file, boot sector, etc.) and then looks for ways to spread. The major things setting it apart from other malware are that it (1) replicates itself and (2) infects other files instead of existing as a standalone file. Viruses can be very harmful (e.g., erasing or damaging files) or they can be relatively benign (e.g., displaying an obscene message to the user on a given date).

Worms do not attach themselves to a host program or file the way a virus does; worms reside in active memory and stand alone with no need for a host. A worm does replicate itself like a virus, but it doesn’t do so by altering files. Instead, it replicates over computer networks.

A Trojan horse program does not replicate itself, and it does not infect other files. A Trojan horse program (or, simply, “trojan” or “Trojan program”) is a malicious program that is contained within, or masquerades as, an innocent and useful program. The most widespread type of Trojan program is the type that installs “backdoor” access to a computer, through which a malicious person is allowed to remotely take control of the infected computer. The next most popular type is designed simply to steal passwords, credit card numbers, online banking data, or other personal information and send that information back to the malicious party. Often, a Trojan program arrives, unknown to the victim, along with a screensaver or game. When the screensaver or game is run, it is designed to then install the Trojan program that is included with it.

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