People hit problems because they don't use the provided uninstaller and instead think appzapper etc. will blast away all traces. You'll be OK if you use the official uninstaller - or at least start with it. This post...
...explains that running the uninstaller is the only thing required.
However if you really want to go on the hunt there is the post below. Note: It's not required and I wouldn't recommend it unless you know what you're doing. The search for system files can bring up all sort of things and block deleting isn't great - be selective if you proceed.
Read it fully:
http://dizaffected.wordpress.com/2013/09/02/remove-sophos-antivirus-system-files/
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Thanks for posting these links. The post from diaffected.wordpress was fantastic for removing a corrupted install of the Sophos Home Anti-virus for Mac. A family member of mine did two full OSX version upgrades, from 10.9 to 10.11 without updating her Sophos client. The client was completely messed up on her computer and would not uninstall using the sophos provided uninstaller. Using the directions from dizaffected, I was able to completely remove and reinstall the Sophos Anti-virus.
Thanks for posting these links. The post from diaffected.wordpress was fantastic for removing a corrupted install of the Sophos Home Anti-virus for Mac. A family member of mine did two full OSX version upgrades, from 10.9 to 10.11 without updating her Sophos client. The client was completely messed up on her computer and would not uninstall using the sophos provided uninstaller. Using the directions from dizaffected, I was able to completely remove and reinstall the Sophos Anti-virus.