I don't think the popup is an actual virus but if you click the window it will download it.
About.blank is just about the nastiest piece of crap that I have ever come across. It is an insideous little worm that gets so deep into your registry that you just can't seem to get rid of it. Even after you think you have deleted it, the bloody thing just keeps coming back.
The first sign is that your homepage changes and no matter how many time you reset it, it just keeps going back to About.blank. Next you start getting popups telling you that your computer is infected with spyware.
The thing is that this still happens when you unplug the internet connection so the program causing it is local.
You can never find it or delete it though because it has "hidden" attributes and is read only.
I tried dozens of downloadable patches to remove it but they all failed to fix it, even those that claimed to be designed specifically with About.blank in mind.
The only program that got rid of it was StopZilla.
If you are unlucky enough to download the worm then go
here to download it.
It is actually a pretty useful bit of software anyway. You get 30 days free trial then you can pay $20 to keep it.