If you search your domain in the Google, or in the integrated Firefox search box, you will see the Google Search result with the alert you've described.
When you click on the alert link (not your site), a subsequent page has a link within it for site administrators. The URL is below:
http://www.google.com/support/webmas...y?answer=45432
You might try using the Diagnostics feature in the VB Admin Panel to search for suspect file versions. If malware has been installed as a file, or if a standard vb file has been modified, it should show up.