Chris Boggs points to the Malware Warnings that Google is serving on specific searches which may lead to sites which are peddling malware :
While searching for a specific keywords or just typing my domain name in Google and after clicking on my site, it generates a warning named: “Malware Warning”. Further they say:
“Warning – visiting this web site may harm your computer!
You can learn more about harmful web content and how to protect your computer at StopBadware.org.”
Chris explains and also suggests reading Matt Cutts’ blog post on Google & Malware:
Malware or spyware is often confused as being something that can only come from opening a bad email attachment. In fact, there are many web pages that contain this kind of additional code, which can cause havoc for your personal computer or even a network you are in. In many cases, sites and pages use tracking software which some would also consider to be spyware or malware. However, in most of these cases there is little damage that the program could do, and it will in fact increase your user experience by customizing your pages to your past behavior.
Lesson, be careful of which sites you link to or downloads you offer from your site as such a warning from Google could seriously harm your reputation and referrals.