http://www.wired.com/2014/08/isp-bitcoin-theft/ Looks like this is an implementation of what I described previously. This guy used BGP to route internet traffic to him — the article is light on the technical details but my guess is that he masqueraded as a popular bitcoin pool and gave out orders that benefited him rather than the real pool.
The problem is that while the base Bitcoin protocol is secure (as far as I know), there are huge ecosystems built on top of it, most of which haven’t had the same scrutiny. The worst I’ve seen is the “stratum mining protocol”: it distributes the mining work well, but I don’t think anyone has paid any attention to its security. There isn’t any authentication of either endpoint: you don’t really need to authenticate the client except for potentially rate limiting issues, but there’s *no authentication of the server*. This means that if anyone is able to hijack your connection to the mining pool, they can ask you to start mining for them, and you can’t detect it until the pool pays you less money than you expected.
I was anticipating this happening with a DNS spoofing attack, but this particular article is about BGP. Doing a MITM of an unencrypted and unauthenticated stream is a very basic level of attack capabilities, and there are a number of different vectors to do it. The Wired article blames BGP, which I think is the wrong conclusion. It’s up to the pool operators and mining-client-writers to come up with some sort of authentication scheme, and then get everyone to switch to it. Until then, it seems well within the NSA’s means to hijack all of the largest pools and take over the bitcoin blockchain if they wanted to.