no ammount of security features will help if you download and look at/open suspicious downloads, we are all our own worst enemies.
i expect the downloads you talk of are LEGAL ones and as such are from a reputable source (if not then maybe this is the time to think about it).
i use AVG anti-virus, Zone Alarm Pro, Start Page Guard, adaware and spybot and i too had to do a restore yesterday as my system was going stupid.
as i said we are our own enemies (im as guilty as anyone else).
cant help much with your problem apart from warning you to be carefull.
as an extra, you could do a online virus/trojan check at click here