Warning about a suspicious application

I have installed a new software and I got the following popup warning: “Wait, this file is suspicious! We run a fast analysis to see if there is any harmful code” (I translate it from Hungarian, might not be exact in English).

Why does it appear?

The publisher of this software is a friend of mine.
What shall I tell him to do to avoid these messages on other computes after installation?

Thanks a lot!

"Wait, this file is suspicious! We run a fast analysis to see if there is any harmful code"
File is supicious and now probably checked against avast cloud

you can upload and test file(s) here > virustotal.com / metadefender.com / jotti.org

you may post link to scan result here if you test the file you have problems with

The publisher of this software is a friend of mine. What shall I tell him to do to avoid these messages on other computes after installation?

Best practises for clean software > https://www.avast.com/faq.php?article=AVKB228