I have a problem with my computer where sometimes when I open firefox or when browsing in firefox a window opens in Internet Explorer saying a securiy alert or something to do with WinAntiVirus pro. I carried out a virus scan using AVG Anti Spyware and it detected tracking cookies which I deleted and also a virus called Trojan.vundo. The same virus plus several others were detected by Norton Anti virus. Norton was able to quarantine all viruses except for one particular trojan horse with filename "sqvsbrox.dll" which is in C:\Windows\system32. I also noticed that after re-booting my computer a notification icon opened saying Explorer.exe is corrupt and unreadable but then disappeared. The same type of message appeared about AVG Anti Spyware but then disappeared. My system performance has also slowed a bit. Please help me solve this problem.