They are the most targetted for the simple reason they present the largest group of users compared to the low percentage of Apple or domestic Linux users.
From time to time I've had people say to me they don't need anti virus as they are careful not to be infected.
The fact is you'll be infected from sources you have little control over, like email, PDF files, web sites, etc.
So you need to protect your computer against these threats.
Try to avoid the many web sites or popups that advertise unknown anti virus products as many are in fact virus or malware themselves and will cause many more problems.
The genuine free anti virus packages are an option but the experience of my customers with many of these products has been poor, essentially you get what you pay for. If I had to recommend one, at the moment, I'd say the Microsoft Security Essentials is very good and also unobtrusive.
Currently I prefer either the Kaspersky range of products or those of Computer Associates (previously known as VET Anti Virus many moons ago).
Using one of these products (two anti virus products installed at the same is an extraordinarily bad idea) and safe internet habits should keep your computer infection free for as long as possible.
These are available directly from the linked web sites or from leading computer stockists.
