Remove Malware/Virus from my webiste

Users are reporting that when they are trying to access my site they are receiving the following message: The website you are visiting appears to contain malware. Malware is malicious software that may harm your computer or otherwise operate without your consent. Your computer can be infected just by browsing to a site with malware, without any further action on your part. I need someone who can fix this issue asap and who knows what the issue is.