Sujay informed me about including details about special scans and the tip for improving scan speed of Avast in this review.

Thanks for the tip Sujay. Ok here comes a small tutorial on how to enable Special scans and Persistent Cache in Avast

Avast has a couple of special scans available if you enable them in Settings>Basic Settings>Special scans

Here is a screenshot showing Avast with the scans available by default

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Now to open Avast's Settings

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Enable the Special scans by ticking the checkbox as shown in the screenshot below

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Now the New scans are available as shown below

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Important Tip to make to speed up Avast scans :
To make the Full System Scan even faster, configure it to actually take advantage of the persistent cache. To do this, open the Full System Scan details, click the Settings button and check the box “Speed up scanning by using the persistent cache” on the Performance page.

Source:
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To go to full scan details:
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Now click on settings for Full Scan:
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To enable Persistent Cache,
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