When the Kerberos elevation of privilege (CVE-2014-6324 / MS14-068) vulnerability has been made public, the remediation paragraph of following blog post made some waves:
http://blogs.technet.com/b/srd/archive/2014/11/18/additional-information-about-cve-2014-6324.aspx
"The only way a domain compromise can be remediated with a high level of certainty is a complete rebuild of the domain."
Personally, I agree with this, but .... But whether this is the real solution, I'm not sure. And the same applies to compromised computers. When it has been identified that malware was able to run on the computer (e.g. scheduled scan found the malware), there is no easy way to determine with 100% certainty that there is no rootkit on the computer. Thus rebuilding the computer might be a good thing to consider. For paranoids, use a new hardware ;)
But rebuilding a single workstation and rebuilding a whole domain is not on the same complexity level. Rebuilding a domain can take weeks or months (or years, which will never happen, as the business will close before that).
There are countless of documented methods to backdoor a computer, but I have never seen a post where someone collects all the methods to backdoor a domain. In the following, I will refer to domain admin, but in reality, I mean Domain Admins, Enterprise Admins, and Schema Admins.
more here..........http://jumpespjump.blogspot.com/2015/03/thousand-ways-to-backdoor-windows.html