“Complaining” in the forums may or may not be noticed, but…

As excerpted from http://www.avast.com/eng/technical_support.html:

If you have any suspicious files that are not detected by the latest version of our antivirus programs, you can send them to virus@avast.com. An ideal way to send such files is to compressed them as ZIP with the password ‘virus’ (so that the attachment is not deleted by some other antivirus on the way).