redmine_clam is a plugin for scanning attachments with using clamav. It adds a filter that automatically scans all attachments upon upload / update and deletes any found viruses. It also adds a rake task that allows you to scan the whole attachments directory on a periodic basis and deletes any found viruses.
redmine_clam is based on ClamAV::Client and uses clamd as the scanning backend.
rake redmine:attachments:clamdscan