spam alert

[Robert]

got a message from my ISP saying that my email address was sending out spam, possibly from a trojan on my pc that was allowing a remote program to access my SMTP server and send email without my knowledge. I was shocked since I'm running ZoneAlarm and don't remember getting any alerts about a program accessing my email. I ran Norton's and it didn't find anything. BUT it was blocking a heap of outgoing emails with "sexually explicit content" after I disabled ZoneAlarm. So ZoneAlarm must be blocking them when it is on, but periodically I turn it off because some web pages don't load correctly when I use ZoneAlarm. Well I disabled ZoneAlarm tonight and right away I got popups from Nortons alerting me that there were sexually explicit emails trying to be sent using my mail account, at a rate of about 20 per minute! I turned ZoneAlarm back on and immediately it told me that IP address 204.152.184.73 was trying to send emails and make a connection with my mail server, which of course I blocked. 204.152.184.73 resolves to freebsd.isc.org. what gives?