Bitcoin has no centre to attack. There is no single organisation or person that controls Bitcoin and transactions don't go through a central clearing house there is really no way a regulator can stop people from downloading Bitcoin wallets and sending each other bitcoins. If there we to block all the websites that people can download Bitcoin wallets from, new ones will come up and some people will compile their own wallets from source code - Bitcoin is like Bittorrent is that respect. If they shut down the internet, people will send each other Bitcoin via SMS and if they shut down the electricity supply, people will use solar and battery-powered solutions