I need to scan uploaded files for viruses on a Linux server, but I'm not sure how to go about it.
What are my options, if any? I'm also interested in how the scanners perform when multiple users send multiple files at the same time.
I would have a look at Clam AntiVirus. It provides a clamscan program that can scan a given file and return a pass/fail indication. It's free and automatically updates its database regularly.
As for integrating such a product into your file upload process, that would be specific to whatever file upload process you actually use.