Actually, most retail computers are becoming standard with an Anti-Virus built in.
Even with, say, "the most sophisticated anti-virus" running, you will still be vulnerable...
There are ways to disable the vshield, as well as trojan being more difficult to detect...

There will never be a way to stop virus writing....
It will only make it a bigger challenge for virus writter...

Look at it this way...
10 years ago, people knew nothing about security...
They'd use common, simple, dumb passwords...
Put the modem number in visual places...
Never think about encryption...
And think nothing about virus scanners...

Now, people use complex passwords (8+ characters, ansii script)...
Hide numbers, unlist em' and so...
People want the highest encryption (128+)
Have virus scanners, up-tp-date info files...
A firewall running (software+hardware)...
And so...

And with all these changes/advancements, hackers still penetrate....
So, no matter the virus scanner power, it'll be beat...