You can use AVG 2013 internet security.
Its free to download the full version as trial package form the owner site.
And the secrete is you can get the key to valid this till 2018 for free, if search the internet.
There is a lots of key hope any of them may work, i have no experience with the free code, as my ante-virus is a purchase copy.
That's your choice. I would recommend you to purchase a original copy.
Hope it will help you.