But does your support ticket allow for the attachment of the samples ?

If not then the physical sample should be sent as outlined.
Or

  • There is an on-line contact form, http://www.avast.com/contact-form.php?loadStyles for: * Sales inquiries; Technical issues; Website issues; Report false virus alert in file; Report false virus alert on website; Undetected Malware; Press (Media), issues.

If reporting a undetected malware, then select that option and using the Browse… button, navigate to the file.