Firewall

So i read the sticky Virus and the Mac thread above.
So one of the ways we are protected is that we have a built in firewall (and the lack of viruses for a Mac).
Well when i checked my firewall it wanst "turned on" we have to do it as it comes turned off out of the box. Does this mean that i was open to threats until I turned it on?
Now that it is turned on does it affect my ability to browse the net/itunes? or is it only stopping intruders and not affecting my computers performance?


Thanks

The fact that it was not turned on "out of the box" is a statement by Apple all by itself about how secure your Mac is. I had the same experience when I got my Mac, and I did turn it on once I found out. But don't worry, you are protected just as a result of the Mac OS X security (most system files can only be accessed by root, not the average user, or anyone who could hack into your system using your userid).

I have found NO impact as a result of having the firewall on.

Thank you for your reply