Resources

Clamby Gem - https://github.com/kobaltz/clamby
Sample Virus - http://www.eicar.org/85-0-Download.html 

(Be sure to disable your antivirus when downloading the file and testing your application)

Source - https://github.com/driftingruby/043-antivirus-uploads-with-clamby

Summary

/usr/local/etc/clamav/clamd.conf## Around Line 8
# Comment or remove the line below.
# Example

## Around Line 101
# TCP port address.
# Default: no
TCPSocket 3310

Gemfilegem 'clamby'

config/initializers/clamby.rbClamby.configure({
  :check => false,
  :daemonize => true,
  :error_clamscan_missing => false,
  :error_file_missing => false,
  :error_file_virus => false
})

If you are raising an error on viruses found, you can rescue from the error in your

application.rb  rescue_from Exceptions::VirusDetected do |exception|
    redirect_to root_url, alert: "Virus found on uploaded file."
  end 

models/uploaded_file.rb  mount_uploader :file, FileUploader
  validate :scan_for_viruses, :if => lambda { self.file_changed? }
  validates :file, presence: true
  private

  def scan_for_viruses
    path = self.file.path
    unless Clamby.safe?(path)
      File.delete(path)
      self.errors.add(:file, "Virus Found." )
    end
  end