This can also be due to some malware attack in your site , you can verify it by doing a Site Inspector which verifies whether your website is malware free or not.
@viscosity : I agree with you and accept your points on security . I oppinion is certificates are one of te security option or features to get safe gaurded.
Website Hacking can be controlled by using SSL certificate which provides a secure web access and avoids these hacking process.
