• Keep your operating system patched.
• Keep all applications patched.
• Critical upates should always be done.

• Install and use Anti-virus software.
• Keep it up to date.
• Scan system frequently (once per week)

• Utilize a firewall to protect computer systems.
• Combination of hardware and software firewalls give better protection.

• Utilize a spyware detection program like http://www.safer-networking.org/ (Spybot-Search & Destroy)

• Only open emails form people you know. Even then, if you are suspicious don't open it!

• Build security awareness training into culture.
• Read about incidents and safe computing practices.

Use software to find and correct vulnerabilities:

• http://www.nessus.org/ (Free scanner)
• http://icat.nist.gov/icat.cfm (Vulnerability Search Engine)
• Microsoft Baseline Security Analyzer