virus - How can I be in danger from viruses and malware?

I have been reading here (in superuser) some questions about the necessity of antivirus software in Windows and some doubts arise.

As far as i know (and imagine) virus software can only be harmful if I download any type of infected executable file and then I RUN IT. I mean that if i have the infected executable in my desktop but i leave it there for years without clicking it, I won't be in danger...

My question is: How can i be in danger browsing the so called "malware pages or sites"??.

If i am just browsing an "infected site" how could I be affected by a virus. In any moment the browser is asking me for the permission to download "something", so how could it be?? Although i don't give permission to the browser to download 'something' is data being downloaded to my computer?? Its some kind of cookie?

I will ask in another way... What is the level of riskiness if i get infected in a malware site compared with the level of an executable virus??

Answer

There are not that many sites that you can get a virus simply by viewing, however there are a few that try to exploit holes in a computer - for example, a while ago there was a nasty one where just viewing a special picture could allow someone to install items on your hard drive (In Windows).

The main reason for the software / services that block visitors to pages is simply to stop the nasty pages that serve no legitimate purpose. For example, there are quite a few "fake antivirus" type websites that the only reason for them to exist is to pretend to be a dialog box and get people to download from them. So, why bother letting people go there at all!

In the above, you are correct that you can only get affected if you actually download and run the software, but why risk it or let it go that far when you can prevent people from visiting all together... For example, I remember some sites that tell people to ignore the warnings, click accept and/or give instructions on how to load addons through the bar in Internet Explorer - it just makes sense to stop people before they are even at the page.

Typically just like email, there is low risk just from viewing, there are a few things that this is not true such as holes in Adobe, Flash and a few other programs, but just don't run .exe or similar files from people or places you do not trust (and even if you trust, take caution!)