I have brought a used desktop computer and I used it for a month without an anti virus software. Then I purchased Avast, after installing it my computer started lagging. Before installing it my computer is very smooth and super fast performance. In avast window it showed that there are few malwares and they are solved after first scanning. But then my computer performance slow downed. When I use Internet Explorer computer hanged after few days my computer is not working it hanges in Windows logo at the time of booting. Its totally a waste product.