K-Lite_Codec_Pack_1635_Mega AV Alert

Kaspersky Internet Security 21.3.10.391 (d) found "Downloader.Win32.WebCompanion.dx" in full installer files following links from this page
https://www.codecguide.com/download_k-lite_codec_pack_mega.htm

The result of checking the downloaded file on VT:
https://www.virustotal.com/gui/file/ceaedd6ef6e5db3bd87576990330201d5498e6f1be97e568a533ce3c3093c8b2/detection

The result of checking the downloaded file on kaspersky.com:
https://opentip.kaspersky.com/CEAEDD6EF6E5DB3BD87576990330201D5498E6F1BE97E568A533CE3C3093C8B2/

K-Lite Codec Pack 16.3.5 Update when downloading clean, the antivirus does not warn about suspicious files.

WebCompanion is an optional offer that can be given during installation. It does not download or install anything unless user gives permission. This offer is only shown during a new installation, and only to tiny percentage of users. It is also a legitimate piece of software.

To summarize. You have absolutely nothing to worry about. The installer is completely clean. The "adware" detection is about an OPTIONAL extra that is only installed after giving explicit permission.