The NSA helps the companies find weaknesses in their
    products. But it also pays the companies not to fix some
    of them. Those weak spots give the agency an entry point
    for spying or attacking foreign governments that install
    the products in their intelligence agencies, their
    militaries, and their critical infrastructure.

That's probably the most frightening thing imaginable, but where is this info coming from? What are the sources on all of these accusations because it feels like a pretty casual mention that all of the hardware/software manufacturers in the US intentionally leave in back doors.