However, if the update is not being successfully installed, it would be hard to "I would uninstall it from my machine, reboot
Not necessarily. It can still be installed, but failed to initialize or had some other problem and did not enable. This may be seen as a failure, but still listed just the same. So it would be interesting to see how listed.
In any case, I would go into Control Panel > Programs and Features, and click on "View installed updates", find KB2393802 and uninstall it, if listed there. Reboot to ensure the Registry is reset and have WU check for updates again and see what happens. Hopefully, if it reports it is still needed, it will install properly and completely this time, and not keep telling you to install it.
Or, you might try Microsoft's Windows Update troubleshooter
In any event, it is a security update, and for that reason, it needs to be installed.
Have you scanned for malware?