Google may temporarily or permanently remove sites from its index and search results if it believes it is obligated to do so by law, if the sites do not meet Google’s quality guidelines, or for other reasons, such as if the sites detract from users’ ability to locate relevant information. We cannot comment on the individual reasons a page may be removed. However, certain actions such as cloaking, writing text in such a way that it can be seen by search engines but not by users, or setting up pages/links with the sole purpose of fooling search engines may result in removal from our index. Please read our Webmaster Guidelines for more information.

https://support.google.com/webmasters/answer/40052?hl=en