Any AV can be free if you look. Most people will mention AVG because its free and is convenient. If you want good ones that are more secure look at Trend Micro, Kaspersky or Nod 32.

Have a good google through all the reviews and make your own mind because the net is full of people who will say "never had any trouble with AVG" or "my best mates dog used it and said it was good" With an Anti virus if you use the internet well then you want it to find things.

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