The best way to stop malicious or misleading sites from engaging in nasty activities with your PC is to not visit said sites in the first place. Most browsers provide a basic level of protection in this sense, warning you if a domain is trusted or not, but there's nothing wrong with putting an extra wall between yourself and the internet and the Web Of Trust (WOT) extension is a good place to start.
The Web Of Trust browser extension is nothing new, however, it was recently updated to version 2.0, which as Nick Peers over at Betanews explains is worth upgrading to, especially if you're interested in provide other users with more accurate reviews of dodgy websites.
Version 2.0 features revamped graphics, but the bigger change is to how users rate the sites they visit. It's been streamlined so all you have to worry about scoring is how trustworthy you think it is and how appropriate it is for children. You'll also have to pick a category -- positive / neutral, questionable and negative.
WOT is available for all major browsers, so no matter how you navigate the web, you'll have the option to at least try it out.