From bleepingcomputer:
How to Temporarily Disable your Anti-virus
AVAST
Right-click on the avast! icon in system tray (looks like this: avast.jpg but orange in color starting with v5). Select avast! shields control and there will be options to disable avast for 10 minutes, 1 hour, until the computer is restarted or permanently.
So! It looks like even though I'm getting that warning, avast really is disabled right now. They told someone else to ignore the warnings and just run it, but I'm hesitating as the thread is from 2011. I think I'm just going to back up and x-out the warning box for now and turn avast back on and wait for your reply.
Again, thank you so much!
Edit: Oh GOD! I clicked the x on the warning box (instead of OK, under the assumption that x would close/cancel it) and now I get THIS!
Warning!! The above realtime scanners are still active but ComboFix shall continue to run. Kindly note that this is at your own risk
What?! Are you KIDDING ME??? Kindly note, ComboFix, that you need a CANCEL button! I'm so SICK of this!!!!
I'm also reading that no one should use this unless they are under the guidance of a malware removal specialist. Not to be rude, but are you one of those?