How should I protect my Windows PC from malware and viruses?

Gwilym isn’t convinced his anti-virus software is worth the money, and wants to know what protection I’d recommendI am using Avast to protect my computer: you recommended it quite some time ago. I am not entirely convinced it’s worth what I am paying, and it is constantly suggesting, in a variety of less than subtle ways, that I should upgrade. What protection would you now recommend? I am prepared to pay for something that works. GwilymIt’s complicated. I’ve spent