The virus threat is not a hoax.  I work in information security and see attacks daily.  That said, if you never launch a web browser, have a good firewall, and never, ever install any software on your computer you'll be fine, mostly.  There are many threats with all sorts of ways for your computer to get malware.  Running a good antivirus program is the best way to keep your computer virus free.  

You don't need to keep the real time AV running if all you are doing is flying FSX.  But you should have the real time checks running if you are reading your email or doing anything with a browser.  Reputable web sites get compromised too.  And you should scan your entire hard drive at least once a month.  Make sure you keep the antivirus updated.

I think all the virus problems were started by the people who make the Anti-virus software.

Create a need and fill the need.

Having said that, I won't go near the web without one.

I've only ever gotten one, but it was bad enough to force me to do a complete system reinstall.

Never again.