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I don't understand very well the difference between viruses ans worms, it seems that worms don't need any host to duplicate himself.

But somebody can explain it? It means that a worm IS a soft? and not the virus?

In case of worms you can find files containing the worm himself? Thanks a lot for responses..

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closed as off topic by soandos, Indrek, Mokubai, kmarsh, Nifle Aug 21 '12 at 22:10

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If you cut a worm's head off, it grows another. Same with the malware variant. – Phoshi Oct 9 '09 at 16:47
up vote 7 down vote accepted

The one thing that distinguishes a Worm from a Virus (and that gives the name "worm" to a virus-like malware), is the fact a worm doesn't need to attach itself to another executable in order to spread across a network.

Worms are thus meant to spread over a network (with or without code meant to damage the computers they infect). Their code is tailored for network spreading. They will always damage the network by increasing the bandwidth usage. Some may even have code meant to provoke denial of service attacks (DOS) by clogging the network bandwidth.

Virus, on the other hand, need an executable image to spread within a system. They will spread to other executables within the same computer (they will attach themselves to those executables which become infected and able to spread the virus). And they spread to other computers as these executables are passed to them by any means (download, on a CD or floppy disk) and executed.

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In essence this is correct, but I'm not sure about a virus needing an executable. I would say that a worm spreads, normally by more than one means. A virus sets up an infection vector that passively waits to be transported. Thus, a worm may transport viruses (and they often do). – harrymc Oct 9 '09 at 17:10
I agree harry. Similarly, a virus could conceivably include code to generate a worm. The classical distinctions are becoming blurred as new methods are achieved. However, I think it is still possible to look at the detailed parts of a... multi-purpose(?) malware and identify them by name if we keep to their modus-operandi. – A Dwarf Oct 9 '09 at 17:55

Worms are computer programs that replicate themselves. Technically, the definition doesn't require them to be malicious.

The definition of virus changes depending on who you ask. To some people, any annoying/harmful software can be called a virus; more strictly, viruses require a host to be sent to a new location.

Here's another page with succinct definitions:

I remembered after posting my initial answer that the IEEE published a formal definition at one point, but when I just Googled for it, the article required a subscription. If someone has IEEE access, or is willing to shell out $19, here's the link:

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A worm is a kind of virus. And what A Dwarf earlier described as a 'virus' is actually called a 'file virus'. There are many types of viruses. Worms, file viruses, bootsector viruses, trojan horses are just a few types of viruses.

So, 'virus' is the general name of unwanted, self-spreading pieces of software. And 'worm' is a specific type of virus.

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