After viewing a few statistics from around the web, I came up with this pie chart to break down which malware infection methods have had the largest effect during this outbreak. Obviously Trojans have the majority. The simplest ways to avoid Trojans is not downloading from untrusted sources on the web, email or P2P, etc. Secondly, be sure to have an up-to-date antivirus with active file protection, meaning it is always scanning new files. This is one of the main factors of antivirus software that can slow your computer down. Most decent antivirus can be set to only scan certain areas, like your Downloads & Temporary folders. This opens holes in your security, but in the end, most of the time it comes down to balancing performance with security to provide the best user experience.