Site hacked Mailware – Help

Hi All

It seems one of my clients sites has been hacked or infected with mailware. I changed the passwords which seemed to work for awhile but now google search have put a mark against my site and blacklisted .

Any suggestions please

Message from google below;

Dear site owner or webmaster of mydomain.co.uk,

We recently discovered that some of your pages can cause users to be infected with malicious software. We have begun showing a warning page to users who visit these pages by clicking a search result on Google.com.
Below are some example URLs on your site which can cause users to be infected (space inserted to prevent accidental clicking in case your mail client auto-links URLs):

http://mydomain .co.uk/
http://www.mydomain .co.uk/
http://mydomain .co.uk/forsale/

Here is a link to a sample warning page:

http://www.google.com/interstitial?url=http%3A//mydomain.co.uk/

We strongly encourage you to investigate this immediately to protect your visitors. Although some sites intentionally distribute malicious software, in many cases the webmaster is unaware because:
1) the site was compromised
2) the site doesn’t monitor for malicious user-contributed content
3) the site displays content from an ad network that has a malicious advertiser

If your site was compromised, it’s important to not only remove the malicious (and usually hidden) content from your pages, but to also identify and fix the vulnerability. We suggest contacting your hosting provider if you are unsure of how to proceed. StopBadware also has a resource page for securing compromised sites:
http://www.stopbadware.org/home/security

Once you’ve secured your site, you can request that the warning be removed by visiting
http://www.google.com/support/webmasters/bin/answer.py?answer=45432

and requesting a review. If your site is no longer harmful to users, we will remove the warning.

Sincerely,
Google Search Quality Team
Note: if you have an account in Google’s Webmaster Tools, you can verify the authenticity of this message by logging into https://www.google.com/webmasters/tools/siteoverview and going to the Message Center, where a warning will appear shortly.