By default Windows XP comes with virtually nothing to protect the system against malware -- save for the Windows Firewall, which is not really an anti-malware system anyway. If you want to do something about malware in XP, you'll need to turn to a third-party product.
With Vista, this has changed, although it's still a subject of broad debate if it's changed for the better. Microsoft's own anti-malware product, Windows Defender, comes installed with Vista and is on by default. If you want to use it, this guide will walk you through the basics of Defender and how to make it work for you; if you'd rather do without it entirely (and substitute in another, Vista-compatible protection program), I'll of course talk about how to disable it. (If you want to disable it now, skip ahead to section 2.1.5.)
