It is not clear how the NSA interfaces with the companies. It cannot use standard law enforcement transmission channels to do, since most use data protocols that are not compatible with that hardware. Several of the companies mentioned in the Post report deny granting access to the NSA, although it is possible that they are lying, or that the NSA’s arrangements with the company are kept so tightly compartmentalized that very few people know about it. Those who do probably have security clearances and are bound by law not to reveal the arrangement.

This arrangement allows the U.S. companies to “stay out of the intelligence business,” one of the officials said. That is, the government bears the responsibility for determining what’s relevant, and the company can plausibly deny that it subjected any particular customer to unlawful government surveillance. Previously, Congressional authors of the FAA said that such a “get out of jail free” card was insisted by corporations after a wave of lawsuits revealed the extent of their cooperation with the government.

It is possible, but not likely, that the NSA clandestinely burrows into servers on American soil, without the knowledge of the company in question, although that would be illegal.