The three most important things in Internet computing, is to keep your Windows operating system up to date with your critical updates from "Microsoft", have some type of Anti-virus protection, and a firewall.

Windows Update:
Windows Update is the online extension of Windows that helps you to keep your computer up-to-date. Use Windows Update to choose updates for your computer’s operating system, software, and hardware. New content is added to the site regularly, so you can always get the most recent updates and fixes to protect your computer and keep it running smoothly.

How do I know if I need an update?
Windows Update scans your computer and provides you with a tailored selection of updates that apply only to the items on your computer. During the scan, a list of categories appears under Welcome to Windows Update and the number of updates that are available in each category is noted in parentheses.

Critical Updates are important!
Any update that is critical to the operation of your computer is considered a "Critical Update," and is automatically selected for installation during the scan for available updates. These updates are provided to help resolve known issues, and to protect your computer from known security vulnerabilities. Whether a critical update applies to your operating system, software programs, or hardware, it is listed in the "Critical Updates" category.

Anti-virus protection and viruses:
Viruses
As always viruses continue to be a problem. You should have Norton Anti-Virus, McAfee, or similar installed in your computer, and updated, so that you are receiving current “VIRUS DEFINITIONS”, if you do not then you WILL get a virus.

Hoax Viruses
These also continue to be a problem. Usually you receive an email telling you to search for a certain file, and then delete it, and then dump your recycle bin. If you receive an email like this, IGNORE IT!  You should never delete any files from your computer. If you delete a file your computer needs it will have to be replaced.
There are lots of websites that help to educate people about hoaxes -- one of the ones I like is http://www.sarc.com which is the Symantec Anti-Virus Resource Center.  There are others.

Firewall:
What is a firewall?
As an Internet user, Firewall protection is a vital component in the fight against hackers, Trojans and automated attack programs. There is plenty of free firewall software available on the internet; my favorite is Zone Alarm.