There are lots of free anti-virus software MOST OF WHICH are not that great as I learned when I visited a friend this weekend. I had a pen drive with me and wanted to use a my portable browser to access the net. The moment the pen drive is inserted into the machine, the resident anti-virus begins scanning the pen drive and after a second or two says it has found a virus. The virus it found? The executable file of my browser. Used any such anti-virus software which can't find viruses or will get you lots of false positives that could have you so worried when in fact there's no threat that should worry you? Do you think it's better for those who use anti-virus software to buy commercial [anti-virus] software because they are better?