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is there any type of viruses can execute by itself after download then on the HDD without clicking on it??

if there is ..... can you refer me to any sites about them?

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5 Answers 5

I think it's more accurate to say 'a virus can't execute itself, unless it has the cooperation of the Operating System and/or software bugs and/or the user.

If the OS allows files to be executed automatically because of their name or location (for example an email attachment) then a virus can masquerade as a legitimate file and be executed by the OS without user intervention. This used to be the default behaviour in early email clients.

Also, if the OS or specific software has errors that a virus can exploit to run its code, then a virus can start itself.

But users are most often the means for a file to be executed. I was surprised recently when a work-colleage told me she thought her computer had a virus after she opened an attachment in an email from a complete stranger. I thought she would have known better.

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Especially when I recognise that name. Thanks for your help. –  pavium Dec 24 '09 at 10:31

Yes, in the context of the browser, since unintentionally you're executing the page without clicking on anything. Such viruses are capable of downloading themselves to your hard disk without your cooperation.

The propagation vector here can be JavaScript, Java, ActiveX, Flash and other plugins. Many such attacks are carried out through cross-site scripting.

You can find lots of information about Web attacks on the site of the popular Firefox extension NoScript.

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The closest example I can think of was the W32.Nimda virus.

One of its prorogation methods was via open windows file shares. From memory, it copied itself as an .eml file to open network shares.

I can't remember the exact details, (and can't find a link in the time I have), but from memory, the file needed very little interaction via Windows Explorer for the code to be executed on the target computer. (I seem to recall just having the file displayed in Windows Explorer was enough for the code to execute).

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offhand, i'd guess that it was taking advantage of Win Explorer's preview functionality for that filetype. –  quack quixote Dec 24 '09 at 9:39
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Yes, as per Pavium's answer, the weakness has to exist either in the operating system or running applications. I remember that an attempt to right click and delete a nimda .eml file was certainly enough to execute the code. –  Bryan Dec 24 '09 at 9:42

Yes there is something called Silent Java drive by (SJDB) that can download and install a virus when you just visit a web page !

You can protect your self from this attack by not installing Java environment or by running the browser sand-boxed.

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I'm unsure ofwhat definitions are standards, but from my limited school level training - no, they cannot by definition. Viruses specifically require the user to run them.

Worms, however, can and do run on their own. And they can do whatever the hacker has managed to do. Whether or not thy can corrupt OS files depends on what vulnerabilities the hacker finds.

Any antivirus maker should have information about them, here are a few (if you think you are infected, please scan your computer)

http://www.eset.com/onlinescan/

http://free.avg.com/gb-en/homepage

http://www.avira.com/en/pages/index.php

http://www.kaspersky.co.uk/kaspersky%5Fanti-virus

..amongst many, many others.

Make sure your O/S is up-to-date, and then you are more or less as protected as you will reliably be without taking extreme measures.

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A worm does not always run on its own. And yes, a virus or worm can install itself without user intervention in case of software bugs or a stupid OS... –  Arjan Dec 24 '09 at 9:29
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sadly, i think the distinction between viruses & worms is purely academic. they're all viruses to the uninformed. –  quack quixote Dec 24 '09 at 9:53
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I guess I was wrong in my earlier comment: it's quite likely that a worm, by definition, executes itself (as part of its self-replicating) without any user intervention at all. –  Arjan Dec 24 '09 at 11:05
    
@Arjan My understanding was that worms in some way are self-replicating/spreading. (Whereas "virus" usually refers to something that entrenches itself in only one system) –  RJFalconer Jan 12 '10 at 19:09

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