Avira are well known for their free tool Avira AntiVir PersonalEdition Classic, which offers good basic protection against viruses, worms, trojans and rootkits. For complete safety you really need the Premium version, though: it has many more features on offer. There's protection against spyware, adware and phishing, for instance. Emails received via POP3 clients may be scanned to block incoming threats. And signature updates are sent through the Premium server, which ensures much better download performance.

The program can also detect many other programs that fall into what it calls "extended threat categories". These could include games if this is a work system, for instance, hacking tools or joke programs. It can also look for executables that have been processed by unusual runtime compression tools. These compress an executable file to reduce its size, and so might have been applied innocently, but they're also often used to make it more difficult for antivirus tools to detect a known malware signature.

There's similar additional protection in the form of heuristic file analysis, that looks for suspicious signs that may indicate you've downloaded something nasty. This kind of technique can deliver false alarms occasionally, but the extra protection it offers against brand new, undiscovered malware means it's still worth using.

Perhaps the best part of Avira AntiVir PersonalEdition Premium, though, comes in its configurability. You're able to create a profile that defines exactly which drives and folders you want to scan, then tweak almost every aspect of the scan itself to ensure it's doing what you need (see the walkthrough), adding a neat finishing touch to what is already a fast and extremely accurate antivirus engine.

Install Avira AntiVir PersonalEdition Premium and it'll immediately go to work, keeping your PC malware-free for six solid months. If you'd like to use the program after that then you'll need to buy a new licence, however. Prices start at a very reasonable £15, which gets you a one year licence that can be used on up to three different PCs. But if you're after real value for money, then we'd opt for the three year deal, which again covers up to 3 PCs and costs only around £35. Visit www.avira.com to order, or take a look at the company's many other security products.