I often wonder if we are digging our own graves regarding technology.  I agree that it is impossible to 100% ensure the security of technological infrastructure.  We have built a society increasingly dependent upon a technological foundation that isn't completely secure.

I think it is interesting--a mark of the times--that the Presidential Security Directive identifies cyber sources as a vital part of vulnerable infrastructure:

These critical infrastructures and key resources are both physical and cyber-based and span all sectors of the economy.

I find it discomfiting that the Directive plainly states an inability to provide adequate and full protection:

While it is not possible to protect or eliminate the vulnerability of all critical infrastructure and key resources ....

This is from Secretary Napolitano concerning the spirit of cooperation necessary in achieving a greater sense of security:

Today, the very nature of travel, trade, and commerce means that one vulnerability or gap anywhere across the globe can impact security and economies thousands of miles away. And that means our security must be a shared responsibility – among governments, the private sector, individuals and communities.

She made these comments in a trip to Australia, underscoring the importance of countries working together to share intelligence to prevent threats.  Among the possible threat types, she listed cyber-terrorism, radical groups and individuals, drug trafficking, and pandemic disease.  She really brings the responsibility for homeland security down to a grassroots level, making individuals and communities be responsible as well. 

Citation:

Napolitano, Janet. "Achieving Security and Privacy." Australia National University, Canberra. 3 May 2012.  

One of the quotations I've learned about and really like is the definition of "critical infrastructure."

"Critical infrastructure" is defined by federal law as "systems and assets, whether physical or virtual, so vital to the United States that the incapacity or destruction of such systems and assets would have a debilitating impact on security, national economic security, national public health or safety, or any combination of those matters."

The critical infrastructure sectors are broken down into the following categories:  Food & Agriculture, Banking & Finance, Transportation Systems, Water & Dams, Energy, Information Technology, Emergency Services, National Monuments & Icons, Defense Industrial Base, Healthcare & Public Health, Communications, Commercial & Chemical Facilities, and Nuclear Reactors.  My quotation was obtained from the Department of Homeland Security's website.

http://www.dhs.gov/files/programs/gc_1189168948944.shtm