The creators of viruses and other malicious software have gotten so aggressive recently, that today its possible to get a "drive-by" virus. You may be at a web site that seems safe, but if there are ads on the site, malicious code can enter your system just by viewing the ads. Unfortunately, the world of viruses is a "cat and mouse" game where the threats escalate as user protection increases.
A solution we have implemented for several clients is "Sandboxie". With this software in place, any code that is written to your system while you are web surfing is placed in an isolated container known as the "sand box". This prevents these programs from making permanent changes to other programs or data on your system. Any malicious code downloaded by the browser can be discarded when your down browsing. You may not even know the malicious code is trying to get on your system, but the "sand box" protects you. You also get enhanced privacy because browsing history, cookies, and cached temporary files collected while Web browsing stay in the sandbox and don't leak into Windows.
This is a great solution to consider to keep your systems safe, and minimize the risk of getting an infection that requires costly clean up and data recovery. No solution is 100%, but by isolating your browsing activity from the rest of your computer, you'll greatly minimize your risk.