This post is basically for site which got demoted due to malware attack or bad html codes.
Sometimes we implement html codes that may affect our site without even knowing.
When your site gets demoted in google search, you do not have to panic but resolve the issue which isn’t and very hard nut to crack.
First thing to do when you receive such message is; you Login to webmasters.google.com and find out the cause or possible cause of the demotion.
Visit your site and remove anything that you deem harmful. It’s advisible to remove the last implementations before you received such message.
After you must have done the above, visit google webmasters again and apply for a review, that’s if you have actually removed all possible causes.
Wait for their reply and get ready for the good news that will get your website back on Google search engine. If you get a negative reply, chances are the problem is still lurking in the dark. Find and remove it then apply for another review.