You can almost set your calendar to Symantec issuing a press release about a new virus threat to worry about. They're not a bad company, but I do question their use of fear tactics to sell more software.
Here's the news article, as it was released to Canadian Press: http://www.canada.com/topics/technology/story.html?id=0e8222a8-aa09-406b-be1c-0bce3e7a2a8b&k=48015 or http://tinyurl.com/2qkwr8
Here's the real information about the virus: http://www.symantec.com/security_response/writeup.jsp?docid=2007-121718-1009-99&tabid=1 or http://tinyurl.com/2wnjkj
Yes, it's a very sophisticated virus compared to what has been seen so far. However, the second link shows that less than 49 people have been infected with it, and Symantec (the people who issued the story to the news services) themselves say the threat is actually Very Low.
To add a little perspective, SilentBanker (as of this writing) does not have a Wikipedia article about it, whereas SQL Slammer, the worm that slowed down the entire internet in 2003, does.
This is an overhyped news story, and so long as you keep your windows patches and antivirus up to date, you will be fine. Also, don't open any unexpected e-mail attachments. New viruses come out every day, and while this one is a clever one, it's not widespread enough to be a serious threat.
A good, free, antivirus program is AVG, and you can get it at: http://free.grisoft.com Just be sure to download the AVG Free Edition, and don't let them trick you into downloading a free trial version of their commercial AVG Internet Security software.