A few good resources for your computer

Free Online Virus Scanner - always up to date - Click on "Housecall" then download the java applet and let it run. The pay version is a good antivirus program. You can search and look up information about specific viruse here.
Adaware - download here then install on your computer. Finds and removes "spyware" that can cause popups and tracking systems left in your system.
Zone Alarm - a firewall, relatively inexpensive - Not the same as an antivirus program.
AVG Antivirus Program - another good antivirus program. Relatively inexpensive.
Windows Update - patches, fixes from Microsoft. This link will show you where to find the update button in IE.