Most terrorists don't use the normal banking system anyway. In the Islamic world, there's something called a "hawala", which is a cash transfer through a trusted individual. Say you're in the US and you want to send $5000 to your family in Pakistan. You would go to a member of your mosque, or another member of the community, and give them the $5K plus "handling fee". That person gives it to someone else who is traveling to Pakistan, again for a "handling fee". The traveler goes to Pakistan, gives the $5K to a guy in Karachi, who takes it to your family. Again, for a cut of the "handling fee". You trust that the full amount is going to get to your family because if it doesn't, the handlers will be f*cked, big-time. Since 9/11, governments have tried to crack down on the hawalas with varying success. For a better explaination, see
http://en.wikipedia.org/wiki/Hawala