My antivirus Avast! (Free Edition) gets rid of viruses provided automatically?

so I have Avast! 4.8 free edition and sometimes I get a Trojan horse on my computer. The same goes for Avast! gets rid of them automatically or do I have to get rid of them? A plzzz

There is no accompanying siren warning and flash on the screen, and you are asked what to do with the virus

Avast Free Antivirus Video Review

Avast! $17.99 Erica J. Vess Avast! - Art Print

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