If you believe your Web site was attacked, do not post in the Joomla! forums. If there is a vulnerability, publishing that information could put other Web sites at risk. Instead, report possible security vulnerabilities to the Joomla! Security Task Force.
Follow a logical and rigorous recovery process
Know the important steps to follow when your site has been compromised. Once you've gotten to this point, there are few shortcuts. (FAQ)
Reset your administrator password
Many attackers take pleasure in locking you out of your site. They do this by 'changing the key', or changing your administrator password. If you are locked out, don't panic! There is a simple procedure for resetting your administrator password. (FAQ)
Find exploit attempts using the *NIX shell
Know how to check for suspicious and/or modified files. Know how to check the raw Apache logs for suspicious activity on your site. (FAQ)