We hosted a moodle website for election watch 2009. Suddenly we received the attached screen stating that either the site is hacked or having the potential to be hacked. The site searched under google also displayed the following warning message. kindly advice us the course of action to retrieve the site.
That's actually Firefox claiming that your site is "bad". I'm not actually sure what it's criteria is but you can probably find out why - and you should.
I certainly would not assume that your site has been hacked. It may, for example, be that spammers (nothing to do with you) are using very close IP adresses.