1) Anti-Virus: Is used to block Viruses, Spyware and Malware and permanently deletes files securely. Free Anti-viruses don't provide real-time protection, meaning you need to schedule scans daily/weekly based on your security purpose. Don't worry free Anti-virus these days can detect viruses as good as any paid software can.
For free anti-virus, I recommend:
2) Spyware: Whether you like it or not, your computer is always at risk of becoming infected with viruses, worms, Trojans, rootkits, dialers, spyware, and malware of every kind. Malicious software is constantly evolving and becoming harder to detect and remove, Spyware is the worst of them all. it can hide in your computer and record your keystrokes and eventually steal your personal information ie., your passwords, credit card information.
For free anti-spyware, I recommend:
3) Firewall: Finally every computer needs a decent firewall to protect unwanted programs from gaining internet access and administrative privileges. A firewall is basically a protective barrier between you and the rest of the computers you are connected to. Most firewalls will alert you about suspicious incoming traffic and also deflects the attack, and gives you a warning about it. But a good firewall will also warn you about suspicious outgoing traffic So the best firewalls do both - tell you about incoming and outgoing traffic.
For free firewall, I recommend:
