A reader writes: Is anti-virus software still the best way to protect personal computers from attack?

Security, as the expert Bruce Schneier (www.schneier.com) likes to say, is a process, not a product: the nature of the threats we try to protect against changes constantly. Lately, the fastest-growing threat has been malware embedded in ordinary Web sites that uses vulnerabilities in visiting computers to download itself and run. Most famously, a hacker installed a malicious Javascript keylogger into the Web site for the 2007 Super Bowl that was designed to give the attacker full access to everything stored on the infected computers – including banking and financial details that can be traded or sold online.

Hackers' motives have also changed: today's hackers are often criminals who are deadly serious about stealing your money. Where once there were thousands of viruses now there are millions, some targeted at niche groups in very specific ways, some operational only for a few weeks before vanishing. Finally, the gap between finding a new vulnerability and exploiting it is much shorter: criminals can afford research labs, too..

Anti-virus software has had to adapt. It has become more sophisticated to counteract stealth techniques and polymorphic viruses that change shape constantly. Today's anti-virus software bears little resemblance to the earliest programs that bore the name. Now, besides using a database of signatures to detect known viruses, such software also uses heuristics to monitor program behaviour looking for previously unknown malware such as rootkits.

The short answer to the question, therefore, is that yes, you should still run anti-virus software and keep it updated. There are good free products available, such as AVG (www.avg.com), and free trials available from Sophos (www.sophos.com). Also, you can get good free online scans from Panda Security (www.nanoscan.com), BitDefender (www.bitdefender.com), and Kaspersky Labs (www.kaspersky.com/virusscanner). But on top of that you should keep all software – especially operating system and browser – up to date by downloading the latest security patches. Be careful out there.