Four steps to protect your computer (Windows)
  1. Check for Windows and Application Updates
  2. Activate Internet Firewall
  3. Install and regularly run Antispyware
  4. Install and regularly run Antivirus on entire system

Attention: The following “All in One”, Internet Security Suites include the internet firewall, anti-spyware and antivirus software (encompassing steps 2-4).
Check for Windows and Application Updates

Periodically download and install current security patches and service packs for Windows, Microsoft Office products and any software that connects to the internet. Systems having the latest patches are far less vulnerable to both local and remote attacks.
Microsoft offers following free tools and information sources
Activate Internet Firewall

Firewalls offer protection from intruders by serving as a barrier between a computer system and the Internet. Pick one of the following:
Install and regularly run Antispyware

Spyware. Spyware is software that covertly gathers information such as user activity, e-mail addresses, passwords and credit card numbers and secretly transmits the information to someone else.
Install and regularly run Antivirus on entire system

Virus. A virus is a self-replicating program, designed to spread from one computer to another, which enters the system hidden within an otherwise trustworthy program or file.