I just reinstalled my windows xp into my dell computer. I ..  

I just reinstalled my windows xp into my dell computer. I downloaded someprograms like the free avg anit virus, and i few other things. I wantedawhile to do a microsoft update idk if that was the problem, but now i amgetting viruses like you wouldnt believe. I run my avg but it keepsfinding them. How are they getting on my computer. Could i havedownloaded a bad avg that is putting viruses on my computer i am soconfussed and i keep getting 4 to 8 virus everytime i go online.