If you want the best free antivirus you can use avast antivirus, where the Avast latest version adds new features.
To activate the avast antivirus license key you can use W6754380R9978A0910-4TZ59467 and can use this license is valid until 2038
Avast does not block the licenses. License may only be used in AV Avast free course and use Avast free for non-commercial purposes. And there is no guarantee of the following license key will be blocked in the future.
Source:
http://tricks-collections.com/avast-license-key-activate-avast-free-antivirus-until-2038/
Update:
New Official Avast Program Update 6.0.1289
Free AV: http://files.avast.com/iavs5x/setup_av_free.exe
Pro AV: http://files.avast.com/iavs5x/setup_av_pro.exe
IS: http://files.avast.com/iavs5x/setup_ais.exe
source: rel=”nofollow” http://forum.avast.com/index.php?topic=84297.0

To update Avast Antivirus, we can use 2 methods or means of Online and Offline.
For the online, after Avast! installed on the computer, usually he has default settings that have been arranged so that each time your computer is connected to the internet, he will renew the database automatically identifies the virus.
But if not, you can arrange it easily. Way, first, of course, open the program Avast! His (usually located in the START »All Programs» avast! Antivirus). For a moment, Avast! will conduct exploration on the memory system to check …