I notice that I haven't had problem with virus. Maybe because Windows 7 is a more secure hardcoded software or As more as we can believe its the antivirus itself.
I have also tried Microsoft essentials. I have post a blog about this antivirus software and it also do Good in terms of my Laptop's performance.
If you want to download the Free AVG antivirus and get a worry free laptop I suggest you download it here.
You can get updates easily on this Free Antivirus.
