No matter how many times this gets stated, it's always worth reading again.

Firefox + Adblock + Flashblock + Tor + NoScript + Linux

I saw this the other day while I was using Internet Explorer. It is rather aggravating. I never see that stuff with firefox... didn't have firefox on that computer. That problem has been fixed now. Anyway, I was only able to get it once, and from the way it behaved, I sincerely believe it was an advertisement with some kind of javascript that took over and redirected the page. It wasn't a virus. It was just a really annoy advertiser who wanted me to install his activex control and scan and tried to do it without my permission, I might add. Thankfully, IE default is now to prevent activex controls from loading without your permission.

Firefox + adblock + flashblock.

It shouldn't be required to use adblock though...it is a serious problem.

I would recommend adding scanning.malware-scanner.com to your hosts file to block that crap.

Flashblock is more annoying than useful for 99% of where I browse.

Tor is good if you're comfortable sending your information through a Tor node which can be monitored (one in Germany I think it was got shut down a couple months ago IIRC) and if you can deal with the slow down. 

Linux is also not recommended to anyone outside of an experienced power user.

Its happened to me, I just pressed the back button.

@fazz/OP

I've had that happen 2 times. It isn't spy-ware or viruses, but it is trying to get you to install some. It appears to be some hijacked ad that is launching a pop-up and shrinking the main window.

Just click the x button for the pop-up and re-size your window and you'll be fine. Or, you can get FF plus adblock pro. If your using IE7, go to Tools->Internet Options->Privacy and click 'Settings' under the pop-up blocker section. Set the 'Filter Level' to high. Don't know how well the IE7 fix will work, but it might help.

Hopefully ioi will get a new ad services. I know a lot of them say ads by Google, but they really seem like crap ads.