Five thousand infected files seem a lot! I think you need to have another antivirus scan your server. I suggest run a xcan with Malwarebytes antirootkit beta. You can get it for free at
https://www.malwarebytes.com/products/ on the web. I think you can use it for either a home computer or a business computer.
I also suggest that you verify the 3 infected files by scanning each one with the free Virus Total scanner on the web at
https://www.virustotal.com/#/home/upload on the web. If not many other AVs besides Clam AV say they are infected, it is probably a false positive detection. You can restore a false positive detections with the QRestore program found in the ClamWin\bin folder.
You should use a good real-time antivirus scanner also. A real-time scanner can prevent infections from getting on your server. Microsoft Windows Defender (for Windows 10 and Windows 8) or Microsoft Security Essentials (for Windows 7 and XP computers) is available for free--it comes with Windows 10 and Windows 8. You can download it for older computers by searching for it on the web. You can use both for business if you have less than 10 computers. I suggest you ran a scan with it--keep it on your computer.
Do not depend upon ClamWin to provide good protection for business compuers. It should be used as a backup, second opinion scanner to a real-time scanner.
You can get more help to clean infections from the ClamWin Antimalware page, available from the main ClamWin web page.
Regards,