What is the Difference Between Virus and Worm ?

[Antrix]

Hello, Yes My Computer was Infected Recently and Several programs do not Work, My Computer was Behaving really Sluggish.A freinds told me I Would Have Got a virus,After installing the Antivirus it Detected Many Virus and there Were Some worm Too ,Yahoo messenger Also Begun To Act to Strangely So I uninstalled yahoo messenger and then I Reinstalled a new version,and it s Working Fine But i Still Dont Know the Difference Between the Virus and Worms ? So can you Please Tell me the Difference Between these Two. Thanks in Advance

[Marco-D]

A worm is similar to a virus by design and is considered to be a sub-class of a virus. Worms spread from computer to computer, but unlike a virus, it has the capability to travel without any human action. A worm takes advantage of file or information transport features on your system, which is what allows it to travel unaided.

The biggest danger with a worm is its capability to replicate itself on your system, so rather than your computer sending out a single worm, it could send out hundreds or thousands of copies of itself, creating a huge devastating effect. One example would be for a worm to send a copy of itself to everyone listed in your e-mail address book. Then, the worm replicates and sends itself out to everyone listed in each of the receiver's address book, and the manifest continues on down the line.

Due to the copying nature of a worm and its capability to travel across networks the end result in most cases is that the worm consumes too much system memory (or network bandwidth), causing Web servers, network servers and individual computers to stop responding. In recent worm attacks such as the much-talked-about Blaster Worm, the worm has been designed to tunnel into your system and allow malicious users to control your computer remotely.

[Steve123]

What is a virus?
A computer virus is a small program written to alter the way a computer operates, without the permission or knowledge of the user. A virus must meet two criteria:

• It must execute itself. It often places its own code in the path of execution of another program.
• It must replicate itself. For example, it may replace other executable files with a copy of the virus infected file. Viruses can infect desktop computers and network servers alike.

Some viruses are programmed to damage the computer by damaging programs, deleting files, or reformatting the hard disk. Others are not designed to do any damage, but simply to replicate themselves and make their presence known by presenting text, video, and audio messages. Even these benign viruses can create problems for the computer user. They typically take up computer memory used by legitimate programs. As a result, they often cause erratic behavior and can result in system crashes. In addition, many viruses are bug-ridden, and these bugs may lead to system crashes and data loss

What is a worm?
Worms are programs that replicate themselves from system to system without the use of a host file. This is in contrast to viruses, which requires the spreading of an infected host file. Although worms generally exist inside of other files, often Word or Excel documents, there is a difference between how worms and viruses use the host file. Usually the worm will release a document that already has the "worm" macro inside the document. The entire document will travel from computer to computer, so the entire document should be considered the worm W32.Mydoom.AX@mm is an example of a worm

[Snake08]

A virus is a program that is designed to spread from file to file on a single pc, it does not intentionally try to move to another pc, and it must replicate, and execute itself to be defined as a virus.

A worm is designed to copy itself (intentionally move) from pc to pc, via networks, internet etc.

A worm doesnt need a host file to move from system to system, whereas a virus does.

So worms spread more rapidly then viruses.

The word 'Virus' has become a common term a lot of people use to refer to worms and trojans too. Which is not exactly correct.

[Spyrus]

A worm is a type of virus that has an important and specific feature; it does not depend upon any form of human intervention to propagate. Since it can replicate and infect by itself, it is by far the most virulent type of virus, and can infect many millions of computers globally in a matter of hours. A standard virus will depend on some form of human intervention to propagate, whether this is opening an email attachment, clicking a malicious link, or transferring an infected disk from one machine to another.
To answer the question as to which is more 'harmful' is difficult, since this depends on the specific 'payload' or malicious function of the virus, worm or trojan. But in terms of rate of infection, the worm is by far the most potent.

[Milton.J]

A Virus is a program that piggy-backs on other programs. It can be attached to a Word or Excel file. Each time the file is run, the virus runs too. It attaches itself to other programs and continues to reproduce.A Worm uses computer networks to replicate itself. It searches for servers with security holes and copies itself there. It then begins the search and replication process again.

[Shen]

What is a virus?
A virus is a computer program that copies itself from one computer to another. A Virus is not a program itself but is computer code that is written into a legitimate document or program. Once this document or program is launched the code begins to run and can reek havoc on your computer. Once a computer has a virus it can do many things including erasing data, and can interrupt the computer's operating system so that it will no longer run. Viruses are often spread by email, either by someone forwarding an infected document to another user or by self-propagating. A self-propagating virus automatically sends email to everyone in the infected computer's email address book. For Lotus Notes users, this is generally not the case. Most self-propogating virus's are writtent to utilize the Microsoft Outlook email technology, not Lotus Notes. Virus's can also be spread from computer to computer via networks.

What is a Worm?
A computer worm is much like a virus but does not need any help from a person to spread. Computer worms spread from computer to computer via networks. Worms exploit holes in operating system security so it is important to download and install all patches.