 Visiting a website with
Microsoft Windows Vista (or earlier versions of Windows) with Internet Explorer allows hijackers to take over your system completely. This is a
Zero Day Exploit and is actively being used on the Internet NOW and has existed in Windows for years.... Microsoft acknowledges they have known about it since December 2006, but have not released a fix.
CORRECTION: Microsoft knew about this in 2004! Way before Vista was released.
Read more here,
here, here
and
here.
The only current Solution: Do not browse untrusted sites or view untrusted e-mails.
Using an alternative web browser like Firefox will not prevent takeover as this is a fundemental Windows Operating System issue.
This exploit is being used to install code that gives outsiders access to
Windows users financial accounts. Online banking with Windows continues to be
a very bad idea.
Windows Vista is not much more secure than earlier Windows it just
costs more, lets you do less and does not run your current Windows applications.
UPDATE: This is a
fix provided by third party (not Microsoft) for this now. | 
