Google said my site is infected with malware and need help to fix this

?I received this mail from Google.
Malware infection detected:http://www.gracester.org/
Unfortunately, it appears some pages on your site may infect visitors with software designed to access confidential information or harm their computers. You may not be able to easily see these problems if the hacker has configured your server to only show malicious content to certain visitors. To protect visitors to your site from malware,Google’s search results now display a warning when users click a link to your site.

Sample URLs

http://gracester.org/
http://www.gracester.org/
http://www.gracester.org/about-us/
Recommended actions:

Register and verify your site in Google’s free Webmaster Tools if you haven’t already done so.
Sign in to Webmaster Tools and check Security Issues to see details of sample URLs that may be infected.
Read our resources for hacked sites for detailed information on how to fix your site.
Remove the malicious content from your site.
Fix the security issue that allowed your site to be infected. Otherwise, your site is likely to be reinfected.
Request a review in Security Issues when your site is clean and secure. Once we determine that your site is fixed, we will remove the malware warning.**********

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I have checked and see this mentioned in security resources:

Malware code injection
These pages directed users to a site that serves malware.Show details
Sample URLs
Last detected

http://www.gracester.org/wp-includes/js/json2.min.js?ver=2011-02-23

Questions : anyone know how to fix this??