Solve "Reported Site Attack" message from browsers

Dear Freelancers Something happen to one of our Joomla websites and it is now showing the message here attached as if our website is a High Risk website Details of warning are here under Need to solve this urgently please thank you in advance ================== Safe Browsing Diagnostic page for [login to view URL] What is the current listing status for [login to view URL] Site is listed as suspicious - visiting this web site may harm your computer. Part of this site was listed for suspicious activity 3 time(s) over the past 90 days. What happened when Google visited this site? Of the 174 pages we tested on the site over the past 90 days, 5 page(s) resulted in malicious software being downloaded and installed without user consent. The last time Google visited this site was on 2009-08-30, and the last time suspicious content was found on this site was on 2009-08-14. Malicious software includes 2 trojan(s). Malicious software is hosted on 4 domain(s), including [login to view URL], [login to view URL], [login to view URL] This site was hosted on 1 network(s) including AS29222 (INFOMANIAK). Has this site acted as an intermediary resulting in further distribution of malware? Over the past 90 days, [login to view URL] did not appear to function as an intermediary for the infection of any sites. Has this site hosted malware? No, this site has not hosted malicious software over the past 90 days. How did this happen? In some cases, third parties can add malicious code to legitimate sites, which would cause us to show the warning message. Next steps: • Return to the previous page. • If you are the owner of this web site, you can request a review of your site using Google Webmaster Tools. More information about the review process is available in Google's Webmaster Help Center.