Hmm, isn't the Korean subnet allocation fixed? If an IP falls in that range, doesn't it belong to the Korean ISP? How can someone be assigned that IP by someone other than the ISP who owns it?
Luckily, AFAIK, BGP is trust-based, so things go to normal pretty quickly.
http://www.ripe.net/internet-coordination/news/industry-deve...
In reality, most ISPs (that I've dealt with, anyway) do prefix filtering to prevent just this sort of thing.
There are rather obvious limits, however, for example you will likely have to believe your ISP C if he says ‘I AM ISP B NOW, TOO’. If you then connect to another ISP D, and tell him ‘I KNOW ISP B’, D will have to decide whether to trust you (likely if you are a large telecom company) or not (if you just happen to have two 10 MBit/s lines to C and D each).
Not quite.