I updated to Sierra and BitDefender would no longer update its database (error -1008). On the menu bar, the icon kept saying "Restart to Upgrade". I restarted multiple times, but it never upgraded.
I tried installing over the existing, to no effect.
Since my subscription was nearly over, I opted to renew, completely uninstall Bitdefender (uninstall app) and install the new download.
The download says it finishes, but Bitdefender is not installed anywhere on my system.