"Hidden" Viruses

[Ansain]

Now, I'm sure you've noticed that, unlike normal programs, viruses tend to not ask your permission before they download themselves onto yur comp. How do they do that?

[mischief]

typically they exploit a piece of software that exists on your computer already. so even if they virus didn't explicitly ask, they 'told' your existing software what to do (download the virus, run it etc).

[automatica]

The following is a fairly good video on why some pieces of malware stay hidden (the music isn't that good though):

http://video.google.com/videoplay?docid ... 2821901542

NB: This doesn't explain how malware gets in without "checks and balances" so to speak, but still interesting none the less.