A webmaster recently wrote an email saying that Google has incorrectly flagged his client's "harmless" website as dangerous for distributing or hosting malware. Though the site still appears in Google organic search results, a prominent warning message saying "This Site May Harm Your Computer" is displayed near the title of the web page.
The website in question has been marked as spam independently by Google though the StopBadWare team has not reviewed the website yet. The webmaster says that his site requires the Adobe Flash ActiveX control and that probably caused Google to blacklist him and trigger the warning.
If you feel that you have a legit site and that Google has wrongly classified your site as harmful, here's how to appeal your case:
1. Check the HTML source of your webpage and make sure that there are no suspicious blocks of Javascript code or hyperlinks that point to bad neighborhoods. For instance, it is not uncommon for hacker to inject code into WordPress Blogs that are not using the latest patches.
2. Since your site is marked as spam only by Google and not by StopBadware, you have to visit this special page to request StopBadware team for marking your site as safe. When both Google and StopBadware have classifed a site as spam, the request for review page is located here.
3. If you are using the Google Webmaster Tools, Google will show you a list of URLs on your site that are suspected of hosting or linking to malware content. Once your cleaned up your site, you can request Google via the Webmaster Tools dashboard (Index Status) to review your site.
If they find everything perfect, the malware warnings for your site are removed from the search pages in 24 hours.
Resources: Stopbadware.org, Google Support, Matt Cutts, Webmaster Central Team