"Microsoft has shipped its final update for Windows XP, which means all the new security holes will not be patched. Nobody knows what will happen next, but malware writers are expected to target the remaining machines. If you are still running Windows XP, it would be a good idea to make it as secure as possible. Unfortunately, there is no "magic bullet". The things you can do to protect XP apply to all versions of Windows. However, because XP will now get more insecure every month, you need to take protection much more seriously.
It's a huge problem. There are roughly 1.5 billion PCs in the world, and NetMarketShare reckons that 27.7% are still running XP. That's more than 400 million machines. Since XP is fundamentally much less secure than Windows 7 (48.8%), Windows 8 (11.3%) or even Vista (3.0%), it's a very attractive target for malware writers. (For comparison, all versions of Mac OS X add up to 7.6%, with Linux at 1.5%.)
The quickest way to make a Windows XP machine almost completely secure is to prevent it from accessing the internet. This works for some business PCs that are used for specific purposes, such as controlling machine tools, but isn't practical for most users. However, an alternative is to install a copy of Linux on the same PC, or boot Linux from a Live CD, and use that for browsing and email. Dual-booting two operating systems is tedious and time consuming, but at least you can get online while continuing to use the XP software that has presumably prevented you from upgrading to a more recent version of Windows."
Keep software updated. This also means switching browsers from IE to Firefox or Chrome, since IE isn’t updated for XP any longer. Ideally, an XP machine wouldn’t have internet access at all, but if you have to make lemonade…