It has been solved.
The domain/script are simple javascript scripts. They now have been tested by third party website and manually reviewed and passed fine.
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.
I think the issue was because of a wider IP block, because of the malware instances for the AS: see: http://www.google.com/safebrowsing/diagnostic?site=AS:3242 (blackhole, Zeus etc. etc.),
polonus
Thank you for this info!
Avast is also listing other script hosting sites that are on tumblr and some tumblrs by itself as malware…