Your site is infected
If Google detects that your site has been compromised, we'll tell you about it in Webmaster Tools (to ensure that you're notified quickly, you can have your Message Center messages forwarded to your email account). If the hacker inserted malware into your site, we'll also identify your site as infected in our search results to protect other users.
If your site has been hacked or infected with malware, you should act quickly to repair the damage. Google recommends reviewing the recommendations provided by the organization antiphishing.org.
Whatever your platform or type of infection, Google recommends the following steps:
1: Quarantine your site
2: Assess the damage
3: Clean up your site
4: Ask Google to review your site
5: Useful resources