computer is sending spam using AVAST?

Hi,
I encountered strange problem. I work in small computer lab, we have network connected to Internet by router. Last days if I format a new computer and then install all the software (windwos xp etc.) from our network, and then install Avast Home, few minutes after restart ashMaiSv icon appears and computer begins to send spam. I formated computer again and installed all software without using network, then connected to internet straight with ADSL modem and installed Avast - everything was OK. It happens only if software is installed from the network - so we have some troyan there. What is strange: spam is send only after Avast is installed. I checked with NetLimiter - if Avast is uninstalled - there is no outgoing traffic from the computer. Avast scan found nothing. Other computers in the lab - with old installations of Avast or with Norton - don’t show any suspect traffic - it happens only with new installations. Any idea - what is it and how to get rid of it - would be greatly appreciated.
Thanks

I think the failing is in the reporting software as it is only seeing the avast internet mail proxy that scan email and then passes it on and not the program responsible for its creation. If it is showing ashMaiSv.exe as the program sending the email, that is the transparent proxy, by disabling that it no longer scans content so you don’t see the email being sent.

You would appear to have a trojan spam bot on your system. There are a number of similar topics on the forums

If you haven’t already got this software (freeware), download, install, update and run it, preferably in safe mode, Ewido anti-spyware

What is your firewall ?
A firewall with outbound checking should notice this connection.