How to quit Avast temporarily?

Here's what worked for me:

1. With the Win+ R combo summon services.msc.
2. Right click on the service Avast Antivirus and click Stop.
3. Before it stops, Avast will warn you that the service is being stopped. Only if you are confident that your computer is safe (and are more worried about the Avast using most of your CPU availability) click the Ok button and the service should stop.

After a couple of minutes of stopping it, I restarted Avast. The load it put on my CPU after the restart was normal (i.e. less than 10%).

Well, here's something you could do.

If on Windows Vista/7: open your start menu, type cmd omitting the quotes, right click on cmd (looks like a black icon with c:\ on it) select Run As Administrator

If on Windows 8+: press WinKey + F, type cmd omitting the quotes, right click on cmd (looks like a black icon with c:\ on it) select Run As Administrator

Once in the Command Prompt it should look something like this:

NB: I use Windows 8.1 Update, yours might look slightly different.

Next, we need to type this:

taskkill /F /IM AvastSvc.exe

This tells Windows to launch a command, taskkill (Task Killer), tells taskkill that it needs to /Force the program closed, and that the /IMage name is AvastSvc.exe

Once done, you can safely close the Command Prompt.