Possibility Sophos preventing upgrade?

Question

I have just tried to upgrade two very different iMacs from Yosemite to El Capitan. Both hang at 95% & I am wondering if the common factor is having SAV onboard, as I read a posting just where someone had an inactive Kaspersky AV programme on his Mac, & ran into exactly the same problems, managed to finally get El Cap installed but then continued with problems until he totally removed the AV 
 Here is the post: 
 forums.macrumors.com/.../ 
 Anybody else run into this problem?

BaybePhace · Answer

We ran into similar issues when upgrading one of our Mac Pros. In our case, we couldn't even boot into the partition created by the Installer. Upon further inspection ia.log contained several references to Sophos (which was installed). Google brought me here, so I signed up to let you know you are not crazy ;-). 
 
Temporarily uninstalling Sophos allowed us to boot into the Installer (after running it from Applications) and we were then able to successfully upgrade our system from Yosemite. Once done, we reinstalled Sophos and everything was good to go. Hope this helps!