Well, yeah, in the end it all comes down to who you're willing to trust. So it's everyone's personal choice.
Personally, the only "web company" I'm willing to trust, is Mozilla. And that's probably the result of the fact that they're not-for-profit. And that fact eliminates a great deal of potential for corruption.
Here you go: http://gigaom.com/2013/06/29/new-prism-slides-say-the-progra...