If you are not getting a virus warning that you believe is a new, undetected virus then if you can zip and password protect ('virus', will do) the suspect file and send it to virus @ avast.com (no spaces).
Or you can also add the file to the User Files (File, Add) section of the avast chest where it can do no harm and send it from there (select the file, right click, email to Alwil Software). No need to zip and PW protect when the sample is sent from chest. A copy of the file/s will remain in the original location, so any further action you take can remove that.
Give a brief outline of the problem (possibly a link to this thread), the fact that you believe it to be a either a new, undetected virus and include the password in the body of the email. Some info on the avast version and VPS number (see about avast {right click avast icon}) will also help.