Have you had any infection on the site recently ?
This is an alert of network shield alert (see image1)
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 you are reporting an FP, then you get another input field open, enter the web URL for the site you wish to submit for review (network shield), etc. A link to this topic also wouldn't hurt.