I received the following message form my ISP, (ATT_, I am on a T-1 there is no server just a router and a few switches and about 75 desktops. Right before I received this message I could notice a considerable slowdown in my Internet speed, which still continues. Have been going from desktop to desktop to try and figure where the problem is without any luck. Any ideas would be great; I know desktops but come up a little short on networks. The x's is my gateway

A host (xx.xx.xx.xx) within your IP block may be
Infected with a Trojan, virus, or worm; or you may have a
Malicious user on your network. The host in question,
((xx.xx.xx.xx) ), is sending unsolicited commercial email (spam).
(xx.xx.xx.xx) is your firewall/gateway/NAT then it is
likely that the offending email is originating from your
Internal network.