Is your software up to date? Do you have automatic updates enabled in Windows, and for any other applications that offer it?
I hope so. Keeping your software up to date is the most crucial element of maintaining a secure PC. Granted, there’s no such thing as “bullet proof”, and attackers will always find new ‘zero day’ flaws to exploit. But, those aren’t the vulnerabilities yielding massive numbers of compromised systems. The malware attacks that generally spread the farthest and do the most damage tend to target flaws that are already known, and that patches have already been developed for.
The truth of the matter is that the fact a patch exists makes it more likely that the underlying flaw will be attacked. Many vulnerabilities are discovered by security researchers or hackers with ethical standards, and are reported to the vendor to be dealt with before attackers even know they exist. Once the patch comes out, though, attackers can reverse-engineer it to discover what the flaw is, then develop an exploit to go after it. If you don’t apply the patches as they come out, you’re exposing yourself to increased risk.
Collecting data from 11 million users, Kaspersky put together an extensive report on the state of vulnerabilities. Kaspersky found that the average user has 12 unpatched vulnerabilities, and that Java, Adobe Reader, and Adobe Flash are the primary culprits. Check out the full report from Kaspersky, and make sure you keep your software up to date.