Ok, I have the same problem, instup.exe running constantly, just started today.
I do not have the folder C:\ProgramData\AVAST Software\Persistent Data on my computer so cannot delete the log file after turning off self defense.
I cannot stop instup.exe in Task Manager. I cannot remove Avast in Control Panel because when I try a popup says the installer is already running.
Avast has hijacked my computer. It is acting exactly like a virus.
I tried restoring my computer to a week ago with no effect. Next step is to restage my computer and NOT USE AVAST!
If you guys did this, please fix it.
If you guys did not do this, somebody has hijacked your program on my computer and you have a bigger problem.