Yeah, I do virus/spyware scans pretty regularly. I was in Ulduar 25 last night and started at around 7 pm server. Had 4 fps at the beginning of the run and by about the 4th boss it started getting better at around 9 fps. Maybe parts of the instance are just more taxing on my video card in combination with internet connection. At home I get 20+ fps all throughout ulduar 25.