recommend
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Avast' - does auto updates everytime you boot up computer and keeps you alerted to dodgy websites. Runs nicely in the background. Been using it for many years.
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AVG Free' is good too. Used that for a number of years on other computers no problems. You need to manually update the virus definitions.
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Malwarebytes Anti malware' is a brilliant bit of kit. It scans in the background and routs out any malbuggers that have attached themselves to any programmes/webpage/links etc.
Well worth having that anyway. No matter what antivirus you are using.
Read a number of reviews on these and they always come out well. As good as and often far better than the big names, Norton, Macafee etc. Though you can upgrade these freebee ones to include more functions - and pay some money. Never felt the need and I've been okay.
So an adult response is:
Download Avast
or AVG Free for anti virus.
Download Malwarebytes for anti malware.
Keep your money for better things - e.g. subscribing to this informative forum