Google released a study last week (pdf alert) suggesting that 1 in 10 web pages could contain viruses that can be forcefully downloaded to your computer. The report says that an average of 8,000 new web sites with malware were developed each week during the month of April.
The take home point here is that we're not just talking about shady websites that you wouldn't trust with your credit card information. More and more often, legitimate websites are being infected with malicious code by hackers. Simply visiting these sites could be enough to allow an attacker to find and exploit vulnerabilities in your system.
Interestingly, the report serves to scare the pants off of its readers by saying "average gumputer users have no means to protect themselves from this threat. Their browser can be compromised just by visiting a web page and become the vehicle for installing multitudes of malware" while they are unaware.
Of course, the simplest thing you can do to protect yourself is turn off JavaScript in your browser, but that could also mean missing out on many rich media features on the web. So the next best thing is to get yourself some good anti-virus/anti-spyware software and run a complete scan every day. You might want to check out AVG Anti-Virus Free and Windows Defender for starters.
http://news.com.com/Google+10+percent+of+sites+are+dangerous/2100-7349_3-6183818.html?part=rss&tag=2547-1_3-0-20&subj=news+++this isn't double threading-is it polonus
http://forum.avast.com/index.php?topic=28380.0click on pic to super-size