One good indicator that your PC is host to malicious software is web browser wonkiness. (Yes, that's the technical term.). But fear not. HijackThis is a freeware tool that "lists all installed browser add-ons, buttons, startup items and allows you to inspect, and optionally remove selected items." The app can help not only disable malware, but to optimize your browser startup. The problem with HijackThis is that it doesn't identify malicious browser add-ons; it leaves the decisions about what to disable up to you. Recommended for advanced users.