Here's how you can check:
On the lower right-hand corner of your screen, you should see (among other icons) a V-Shield (a shield with a 'V' on it) and a magnifying glass. Right-click (click with the right mouse button) and select 'About' from the menu.
If the 'Created on' date is more than a week or two old, you need to update your virus scanner and set (or reset) an auto-update schedule.
If you don't see a V-shield or a magnifying glass icon you defintely need to reinstall your anti-virus software and make sure that it is running and updating regularly.
Detailed instructions can be found at:
Viruses and Anti-virus software on the
ISU Extension Information Technology web page.