The "This site may be hacked" notification cannot be removed until the website owner or administrator of the site takes action. Full details from Google click here: https://support.google.com/websearch/answer/190597?hl=en
Try these steps to fix your website:
1. Register and verify your site in Google’s Search Console. https://www.google.com/webmasters/tools/
2. Sign in to Search Console
3. If the website is not present add the site as Add A Property
4. Add the URL and Verify by downloading and uploading the HTML verification file to the root directory of the website.
5. Navigate to the Website in Webmaster Tools, click check the "Security Issues" section to see details of sample URLs that might be hacked. Fix the security issue that allowed your website to be infected. Otherwise, your site is likely to be reinfected.
6. Read our resources for hacked sites for detailed information on how to fix your website.
7. Request a review in the Security Issues section in Search Console when your entire website is clean and secure. After we check that your site is fixed, Google will remove the "This site may be hacked" message.