I would personally recommend
Microsoft Security Essentials.
Good articles:
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Stop Paying for Windows Security; Microsoft's Security Tools Are Good Enough
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Microsoft Security Essentials Ranks as Best-Performing Free Antivirus
Some people have the "best" security, yet still get viruses. Why? Because most people are uneducated on internet security, which is why viruses are so widespread.
Personal understanding is much more important than any software you have. I used to get viruses, trojans, etc., but since my understanding of internet security has got better, I've seen barely no harmful files reach my computer.
Once you know the difference between good and bad, such as understanding why you shouldn't click on particular links on emails, the web, instant messenger, etc., you'd needn't have such bloated security software.
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