system
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my sister do a lot of online payments, she used my credit card in a lot of shopping websites, Now I have setup Avast free antivirus on my pc is it enough to protect my data from hackers and other threats?
Yes.Pls use Avast SafeZone Browser’s bank mode option. 
And to tighten security we recommend to change these ( default ) settings :
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Avast - Settings - General - and check : Enable Hardened Mode - Aggressive.
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Avast - Settings - Components - Webshield - Customise - Main Settings - and check : Warn when downloading files with poor reputation.
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Avast - Settings - Components - Webshield - Customise - Main Settings - and uncheck : Do not scan trusted sites.
Greetz, Red.