If your website needs to allow visitors to upload files that may later be downloaded by other visitors, then your site should definitely be checking those files to verify that they do not contain any viruses or other malevolent code. Fortunately, using the ClamAV module, you can add the open source ClamAV antivirus software to your site. The module documentation briefly explains how to install the virus scanner if you have control over the server. (For shared hosting, you would need to request the web hosting company to install it for you.) The module will examine every file that users try to upload, and if the ClamAV scanner detects malicious code, the file will not be saved on the server.