How the Bitcoin community will handle attacks on a Client's code? I have some thoughts about the following scenario.

The brightest future.

The Bitcoin becomes a very popular and liquid currency all over the world. Some serious financial or political parties may become unhappy with this fact - they may have no influence on an Internet or may be unable to publish new laws. Since the major support of the Bitcoin infrastructure comes from the logic of its official client. And the easiest way to shutdown the network, as I can see, is to compromise the client itself. Someone may:


Buy the Github at once and quickly release new malformed version of the official Bitcoin client.
Bribe one of the trusted developers to sabotage the client code.
etc.


It doesn't seem so impossible, if someone with a big money would really want to stop the Bitcoin, even if everybody else will like it.

The question is


Is it possible to technically shutdown the whole Bitcoin network - with reasonable efforts and abilities to replace official client?
Are there any Central Trusted Authorities, that may verify any arbitrary client out there for it's correctness about the Bitcoin Protocol and, thus, prevent my scenario?




Note: I don't mean the situation, when someone will accidentally place an untrusted line in the client's code, and this fact will be overplayed to weaken the trust in the Bitcoin. I mean the situation, when the compromised client will irreversibly destroy all the system - leaving no viable ways to recover it.
FYI since BTC mining became so prohibitively expensive due to use of ASICs 1 51% attack could be pulled off at any time by BTC Guild. Their listed % is just under 50% at ~48% but I find it hard to believe they aren't sitting on >51% mining power. See the problem is every client is meant to be able to mine making large conglomerates like BTC Guild impossible.
This could very well be the end of BTC since you've got no change at all of mining BTC using anything but an ASIC pool.