Security software needn't cost the earth. Here's five internet security tools that are free and work very well.

Microsoft Security Essentials 2.0

Microsoft Security Essentials is a complete security package which has been designed to offer protection against a wide range of different types of malware.

Real-time protection sees the program constantly monitoring your computer for signs of suspicious activity which may be indicative of a malware infection, while scheduled scans help to ensure that your hard drive is free from viruses and spyware at all times. Any suspicious items that are detected are automatically moved into quarantine where they cannot cause any damage, and regular updates helps to ensure that the program offers protection against all of the latest threats.

Avast! 6.0.1125 Free Edition

Avast! 6 Free is an antivirus package that's so packed with extras that it feels more like a security suite.

And so, of course, the program can scan selected files, folders, or your entire system, either on demand or your schedule of choice. While the boot-time scan runs before Windows loads, and accesses your hard drive directly, so bypassing Windows own drivers and helping you detect even the stealthiest of rootkits.

Comodo Antivirus 5.4

Comodo Antivirus 5  is a powerful antivirus tool that uses multiple layers of protection to keep your PC malware-free.

A new behavioural scanning system watches running processes for suspect behaviour, for example, uncovering even zero-day threats before they can cause any damage. And new cloud-based systems see application white listing and some malware detections done in the cloud, allowing for greater accuracy, less false positives, and a faster response to new threats.

AVG Anti-Virus Free Edition 2011 v10.0.1375

AVG Anti-Virus Free Edition 2011 is the latest version of AVG's popular malware detector. At the program's heart is a strong core antivirus engine, which monitors incoming and outgoing emails, as well as every file you access, detecting and blocking threats before they can cause any damage.

BitDefender Total Security 2012 Beta

BitDefender Total Security 2012 delivers a first look at what's going to be a very comprehensive security suite.

The lengthy feature list includes everything you'd expect, then: strong antivirus, an accurate spam filter, configurable firewall, browsing protection, and multiple layers of real-time protection to catch malware before it's able to cause any damage.