Error messages

Hello.

My (Mac) computer suddenly started throwing up two error messages out of the blue. Can someone tell me what these mean and what I am supposed to do?

The first one: “System Extension Blocked. A program tried to load new system extension(s) signed by ‘AVAST Software a.s.’. If you want to enable these extensions, open Security & Privacy System Preferences. Open Security Preferences. OK”

The second: “System Scan is recommended.”

Thanks,
Michael

Mac section is here >> https://forum.avast.com/index.php?board=5.0