While it is easy to point the finger at the banks and other sources,...look at your computer.
Do you have spyware installed on it?
If not, go here.
http://www.download.com/Security-Spy...0.html?tag=dir
I run Adaware and Spybot. I also have Zonealarm, but I don't use that one often, just out of personal preference.
http://www.download.com/Ten-Spyware-...ml?tag=nav_dir
You may have spyware/trojan horse transmitting your info.
Also, use an anti-virus program. And turn on your firewall.