I was just on line and this ad popped up saying congratulations, it would enter me in a drawing, etc. if I’d click on the OK button. I was not about to click on it and could not get rid of it. There was no x on it or any way to get it to close. The screen froze and nothing worked. I couldn’t close or back my way out of anything. I went to the apple icon and told the eMac to restart several times but nothing happened. It would not shut down either. I finally hit the power button to turn it off, but the little light on the front of the machine stayed on and when I restarted and clicked on the Safari button the same adware screen came up and everything froze up again. I finally just unplugged the power cord because there was no other way to get out of it. This is my first Mac, and I got it a few weeks ago. It’s an eMac running Tiger. How do I keep this from happening again? Edited to add: I haven't downloaded anything or done anything foolish. I was reading Dear Abby on line when it happened. I've had ad popups before on this machine, but this is the first time they've frozen the computer.