I checked some domains back links and domain authority. In Moz site explorer shows DA, PA and SS. Why some domains has more than 50 percentage Spam score. How it's happens
Aneesh check your domain linked from gambling sites
The importance of backlinks in search engine optimization is well known. The number of bad links are actually responsible for the spam score. The importance of Spam scores are noticed by search engine optimization research company called Moz. Actually It not directly related to do with Google. This can be seen as a warning that Google may impose a fine. Real good back links reduce spam score.