Badware is bad and Google does not approve of it. Google has done a great deal to help protect its' users from malicious software.
Google shows a warning page prior to directing a user to a webpage that has been identified as using badware or any intrusive and dangerous software. It will show you, before you even leave Google...
If you click on a Google result that states "This site may harm your computer" then Google will display a warning page...
Badware and the new webmaster
For most of you reading this there will be no need to worry about this guideline. In order to have malicious software on your webpages you pretty much have to specifically put it there knowingly. If you are doing this you not following the Google webmaster guidelines.
There does exist a danger for the new webmaster of unknowingly placing badware in your web pages, or being hacked and having such software placed on your servers without your knowledge.
To understand fully what makes a site a "Badware" site you can look to the StopBadware.org Guidelines (yes, they have guidelines too).
What to do if you find that you are being affected by this warning screen
Google uses the information provided by StopBadware.org to determine which websites receive a warning screen. If you find your website has such a warning screen, it is important to find out what the problem is, then fix it, then let StopBadware.org know you have corrected the problem.
The Google help pages state that "All appeals and reviews are handled by StopBadware.org. Please send an email to email@example.com explaining why you think your site was mistakenly identified or how you have modified your site. They will investigate and contact you with their findings. If they determine that your site does not spread malicious software, they will inform Google, who will remove the identification from the search results."
Google will let you know the specific problem if you are taking advantage of the Webmaster Tools.
It is particularly rough to find out you are being affected by this problem, and in the past it was very difficult for a new webmaster to identify the "badware" within their website. Google will alert a webmaster via the Webmaster tools diagnostic summary. They will also attempt to alert webmasters via email.
by Patrick Sexton