Trend Labs shares defensive approaches for targeted attacks where a specific group of users might be selected to compromise corporate security controls:

http://blog.trendmicro.com/trendlabs-security-intelligence/understanding-targeted-attacks-how-do-we-defend-ourselves/

QUOTE: Remember that even though we’ve come to accept that attackers have greater control, does not mean that we don’t have any of it. We do, and it is important to take note of that because using that control is highly critical in dealing with targeted attacks.

1. Control the Perimeter

2. Deploy Inside-Out Protection

3. Assume Intrusion and Act Accordingly