I help manage a small network of about 40 computers. We are running an Exchange 2003 mail server.
What is the best way to find which machine is infected by a spambot? I've tried installing anti-virus and anti-malware programs on each computer. After scanning the computers I did find a few that had lots of malicious programs and thought that our problem was solved. However our domain keeps getting blocked by DNS Blacklists and I have to remove them daily for our clients to receive our e-mail.
Note: We are being attacked by Directory Harvest and Backscatter tactics.
edit: Our e-mail server doubles as a DNS server. Could this possibly open up vulnerabilities for spam attacks?