Avast! 4 Home edition.
Common belief is that good antivirus programs does not come free.Avast is an exception. You can trust this award winner. Avast features a powerful resident module that is able to detect a virus before it has any chance to infect your computer. File system protection ensures that no virus will be started on the computer.It is always better to use a firewall also as the first line of defence and Comodo firewall is a good choice.