If you see this message on the Manual Actions or Security Issues page in Webmaster Tools, it means that Google has detected pages that appear to have been hacked by a third party. Often a hacker will upload files or modify existing files, which then appear as spam in our index. In many cases, this malicious content is hidden through a process called cloaking.
To protect users, your site's pages may be labeled as compromised or may not rank as highly in our search results.
Recommended actionFor a comprehensive list of what you can do if your site was compromised, please refer to http://www.google.com/webmasters/hacked.
Once you’re sure your site is no longer compromised, request reconsideration of your site. After you’ve submitted a reconsideration request, be patient and watch for a message in your Webmaster Tools account — we’ll let you know when we’ve reviewed your site. If we determine your site no longer contains problematic content, we’ll remove the compromised warning from our search results.