The following URL can be used to check a site for malware:
The diagnostic url works to check any site, replacing the domain at the end with the site you wish to check.
Eek my site is serving up malware!
This page has some info on what to do if your site has been infected:
Reporting malware sites
Here are some additional links that are helpful to report a site which is serving up malware or a site that is incorrectly listed:
Report phishing URLs:
Report phishing URL false positives:
Report malware URLs:
Report malware URL false positives, or request a review after your site is now clean:
And if you want to get fancy, there is of course an API to incorporate google’s database to your own use: