How quickly should an anti-virus programme warn me of a virus on my computer?

When a virus warning appears on my computer, does that mean it has got into my PC that very moment, or seconds before, or much earlier?

I'd like to know this, because if a warning is displayed, and I have been looking at a website for several minutes, I would suspect that the virus has come from that website. Or, if I open an email, and a virus warning pops up, I would guess the email let the email into my PC.

If anyone knows the answer to this question, it would be a great help to me, and probably many other people as well.

So, THANKS!!! to anyone who can help us out with this one.

How quickly should an anti-virus programme warn me of a virus on my computer?antivirus scan

It goes on what AV your using - which are you using ?

If you wish to test out your AV then go to this site:

http://www.gotovni.com/help/UninstallAOL...

A good AV wont let you enter - it has a worm.

How quickly should an anti-virus programme warn me of a virus on my computer?computer security

it depends on your virus software but most give you a warning as soon as there is a threat.
It's really hard to say. It depends on which anti-virus software you are using and how often the software updates its definition. Sometimes it takes long for some companies to get the virus def out. I would say Norton or McAfee are pretty good in this case.
depend on virus.

Anti Virus will warn when a recorded virus arrive into your PC.

some only warn when they start activity( because some new virus will go into it and do nothing until some time...)