The internet simply isn't safe any more. Along with the reams of useful information are hazardous viruses, worms, spyware and other malicious software.

Featured regularly in our downloads section, the fourth edition of Avast is the latest in a growing list of security programs available to download and use free of charge.

The old adage that 'you get what you pay for' is one that usually applies to computer software, but Avast has incorporated a number of features you'd normally only expect from a paid-for application.

As well as the standard virus scanning and real-time, always-on protection, it has a shield for file-sharing applications and instant messaging programs. This will give some protection when sharing files on sites such as Kazaa (although we don't endorse such activity), and when receiving files via MSN, Yahoo or AIM instant messaging services.

One of the best ways of keeping your PC protected is to use a firewall. Windows XP has its own free firewall, or users can choose the free Zone Alarm tool. As an added layer of security, Avast provides a Network Shield that acts as an intrusion detection system.

This is no substitute for a firewall, but it offers a basic level of protection against some web threats. Those using a broadband router may already have a firewall up and running.

We found the software very easy to use. When you first fire it up, Avast 4 gives you a set of five steps to follow to ensure your PC is virus-free. It then maintains itself without requiring much input.

Our only real gripe with the menu system was the lack of clear icon labelling. A small pop-up dialogue box appears if you hover your mouse cursor over each one, but tracking down the feature you need can take time. It will, however, download an antivirus update whenever there's one available, meaning that you should always have the latest protection.

Understandably, Avast 4 is not as feature-rich as a full, paid-for antivirus package, but it does the basics really well. Provided you exercise a degree of caution and common sense when using the internet, and ensure that the automatic virus update option is activated, it should serve you very well.

If you decide to try Avast, remember to run only one antivirus package at any one time. You can download the software by clicking here.