Under the proposal, which is being informally circulated throughout the department and the Department of Homeland Security, the NSA could set up equipment to look for patterns of suspicious traffic at the internet service providers that the companies' networks run through. The agency would immediately notify the Pentagon and the companies if pernicious behavior were detected.
Oh wait, there is a suspicious traffic detector for the private sector. It's called EINSTEIN. The Department of Homeland Security is currently running pilot tests on EINSTEIN 3.
Source: The Atlantic