What are the dangers of possible Mac OSX backdoor?

Question

Many people say that Mac OSX has a backdoor in it. It probably does, why wouldn't it? It's closed source therefore it would be stupid for Apple not to put in a special access route.

The question is what implications does this have on anonymity/Tor? Let's say you're running VirtualBox with Whonix with a Mac OS X host, what's the danger in that if,

1. No important information is stored on the computer

2. The computer is only used for Tor to browse the internet and that's it

Can somebody explain what the dangers are during normal browsing (through Tor) even if a backdoor is present? Why would an open source host make Whonix and VirtualBox safer? Again, this would obviously be different if actual data is stored on the system and could therefore be looked at or stolen. However browsing is fairly amnesic. I think the problem is that I'm not understanding how a computer can be attacked during just browsing the web through Tor.

Answer 1

Why would an open source host make Whonix and VirtualBox safer?

Less likely to include a backdoor?

Open Source: Security by openness / correctness [see wikipedia]

Closed Source: Security by obscurity [see wikipedia]

The question is what implications does this have on anonymity/Tor?

Generally it can be said, anonymity requires security.

It depends on your threat model. Whom you're hiding from. If you adversary has access to the backdoor, depending on the type of backdoor, you cannot hide from that adversary. If you just want privacy from search engines and such, they might not have access to the backdoor / not using it, in that case, no big difference.

You can make up theoretic cases were the backdoor matters or not.

Let's suppose(!) [pure speculation / thought experiment] there was a [hardware] backdoor, that logs key strokes and/or desktop screenshots and communicates them by modifying the timing [or...] of outgoing TCP packages. If an ISP knew about that backdoor and was passively eavesdropping, you would have no privacy at all. When that ISP is also the one you want to hide from, you see now why you're better off not having a backdoor.