When a new system joins a domain, the domain administrators group is added to the local administrators group on that system automatically. This ensures that domain administrators have full access to the newly connected system. Unfortunately, this also means that the system is vulnerable to high-level malicious code attacks.
If a domain administrator is logged onto a member system while malicious code infects the system, that code assumes the privileges of the domain administrator. Thus, the code obtains local administrative privileges over the member system.
While this is a problem for all member systems in the domain, it is especially problematic for those workstations employed by your administrative personnel. End-user client systems are rarely accessed by domain administrators as to make this vulnerability a minor concern. However, administrative personnel often log into their own workstations as domain administrators in order to perform domain level administrative tasks. This occurs on a much more frequent basis and thus increases the risk to their local systems. Once malicious code obtains local administrative privileges, it can effectively take over the system and possibly infiltrate the entire network.
One precautionary measure against this problem is to remove the Domain Admins group from the local Administrators group via GPO applied to the OU that houses those specific workstations used by administrative personnel. With this change, malicious code infecting a system while a domain administrator is logged on will not automatically gain local administrative privileges to the system.
You should also avoid running applications and services using administrative accounts (especially domain administrative accounts), on the workstations employed by administrators. Such applications and services, if compromised or already hosting a Trojan horse, may grant those programs unrestricted access to your entire domain.
James Michael Stewart is a partner and researcher for ITinfopros, a technology-focused writing and training organization.