It could be a virus trying to disable Avast. I had one that disabled Norton once.
Or, it could be a scam. Sometimes pop-up windows will claim you have a virus and tell you do call a number or download a program to stop it.
Try doing a full system scan with Avast and then post the results, ok?
Avast smart scan as follows:
We found some issues**
Viruses and Malware We didn't find any viruses or malware
**Software updater Some of your software is not up to date
Browser Cleanup You have no bad add-ons in your browsers
Home Network Security You have no compatibility problems
**Performance Issues Your PC's performance needs optimization Resolve ALL
(this is a button to click) Rescan
I did not click the resolve all button... yet
I also ran, waiting for a reply to this
Malware Bytes anti-malware.... All came out OK