I asked Avast about this problem, but since they don’t provide support to free users I have to post this here.
So, here’s what I originally said:
“I had Sophos Home for Mac up until I heard about your antivirus and saw what it was like, then instantly dumped and uninstalled Sophos, then I tried to install Avast Mac Security until I was met with an error saying that Avast was incompatible with Sophos and since I had it, Avast couldn’t be installed, even though there are no traces at all that it even existed on my Mac. Please help.”
By the way, I used the bundled uninstaller, I didn’t just drag it to the trash.
I remember there is a thread on this webboard where someone from avast told what was detected, but I’m not sure if it was about Sophos or another av.
See if you can find it I would say.
In the mean time I will try to get a hold of someone from avast and ask him/her to have a look.
Avast detects loaded kernel extensions (KEXTs) of the other antiviruses. If a Sophos
kernel extension is still loaded, Sophos was not correctly uninstalled. If you run the kextstat
command, you should see a sophos KEXT loaded amongst other KEXTs.
I would try a reboot first. If the KEXTs will be still present, than Sophos did left more mess than expected
and searching for the loading mechanism of the KEXTs is necessary. Most probably there will be some
launchd plists left in the system together with the KEXTs self.
You can also try asking Sophos technical support how to clean your Mac if their product is not capable
doing it by itself