Spyware help!

[Xylochick216]

I have no clue what happened to my computer today, but I got on this afternoon and there's a blinking triangle with an exclamation point in the taskbar of my computer that keeps saying, "Warning! Your computer could be infected with spyware! Click here to find out how to get rid of it." I know it has to be spyware itself. I usually use Firefox, and that's fine, but in explorer, my homepage is now "about:blank" and keeps going to random anti-spyware sites even when I try to reset the homepage to yahoo. I've run my virus software several times (which found 4 files to quarrantine) and I've run both spybot and adaware, which each find a few things each time. I went through the add/delete programs in the control panel, too, and deleted anything that I didn't remember installing. It still keeps popping up and flashing in the taskbar, and random explorer windows keep opening with adult pictures and anti-spyware ads. Anyone have any suggestions as to how to make it stop? I'm at my wits' end!

ETA: I've also tried right-clicking on the flashing triangle, and no menu pops up or anything.