Make sure that automatic software updates are turned on.

Most malware will attempt to take advantage of known exploits (holes) in software on your PC or Mac. By having your machine scheduled to automatically check for new updates every day you will protect yourself from many malware infections.

Note: many people in the world do not have a valid Microsoft license for their Windows software and therefore are not able to turn automatic updates on, nor download new updates to their Windows software. Those who create malware know this, and take full advantage of the exploits (security holes) that exist on those PCs that don't do Windows updates. If you don't have regular updates applied to your PC or Mac, NONE of the rest of the security measures can fully protect you enough from malware that takes advantage of know software exploits!

To configure a Windows to check for updates you would click on the following path:

Start --> Control Panel --> Security Center (or just "Security" in Windows Vista)

The screen would look something like this in Windows XP:

Windows XP Security Settings

Also note: that other products that are regularly used could have the need of being updated to avoid exploits (security holes) within that software. Some common examples might be: