Copied from the Financial Times today:
It is designed to be secretly downloaded to a person's computer, where it will lie in wait until a user tries to connect to one of several banking websites. The "Trojan horse" software then springs into action, hijacking the computer's web browser and displaying a fake log-on page. Barclays and Bank of Scotland are two of several banks targeted by Troj/BankAsh-A, according to security software firms.
The fraudulent web pages are so convincing that the user's address bar indicates he or she has logged on to a legitimate banking site. When the victim types in his or her account information, it is recorded and sent to a remote computer.
"You already couldn't trust the sender address on incoming e-mail. Now you can't trust the address bar in your browser," says Scott Chasin, chief technology officer at MX Logic, a security software company.