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Avast: Enable detection of potentially unwanted software

The Avast antivirus detects viruses and malwares, but it is also able to protect you against adware and unwanted (search bars, intrusive adware, etc.) programs.

This option is not enabled by default. Here's how to activate it.
Open Avast, go to "Resident protection", "File Agent" and click on "Expert Settings
In the "sensitivity" section, select "Find potentially unwanted software (LPI)"
Repeat the operation for the other agents.