I downloaded 5.0377 free last week and installed over 4.8 on my XP SP3 and my computer started to crash, completely lock up. Had to hold power button, control alt delete didn't work. Decided to uninstall using an uninstall program. It started back up, No indication program was on computer in windows uninstall. Could not use System Restore, went back a month of points and no luck. I then reinstalled 5 and an uninstall window came up and clicking that uninstalled the program. I downloaded and reinstalled 4.8 and everything is working again. I hope someone at Avast is monitoring this forum. Avast 5 seems to be a disaster at least on XP. Been using avast for may years. I will not upgrade to 5 until Avast updates and everyone here checks it out to be OK.