Microsoft have issued several security updates for Internet Explorer 7. As exploits go, this one appears to be quite serious as they note that “consistent exploit code can be crafted easily”. This means that another outbreak of (possibly virus-related) attacks looks imminent.
If you use IE7 and don’t have automatic updating enabled, you should check for updates and install it manually. Instructions for updating your Windows Vista or XP computer can be found on the Microsoft Update page.