I need our malicious code removing from our website.

We have received the following message from site grounds.

"We would like to notify you that a malicious code was detected on your website and and a huge number of email spam messages originating from it. In order to prevent further malicious activity from your account we have limited access to it, because malware is a serious threat not only to your account, but also to other accounts in the same infrastructure."

We need this repairing as soon as possible.