Google has built automated scanners that detect malware on websites we’ve indexed. Pages that are identified as dangerous by these scanners are accompanied by warnings in Google search results. Chrome, Firefox, and Safari browsers also use our data to show similar warnings to people attempting to visit suspicious sites. Webmaster Tools now provides webmasters with samples of the malicious code that Google’s automated scanners detected on their sites. These samples typically take the form of injected HTML tags, JavaScript, or embedded Flash files. Read more about this process in the previous post on this blog.”]
Source: https://security.googleblog.com/2009/10/show-me-malware.html