50000 spam message being sent

My Hosting company axed my site temporarily because someone hacked it and is using it to send out 50000 messages within a few minutes. Where do I need to look to figureout what's been messed with. I asked my hosting guys which script was running and they couldn't tell me. Any help would be greatly appreciated...

Admin, if needed I can PM you my account info for my hosting so you can peak around.
Tim

You need to find out how hacker is sending mails. This can be found with mail server log. csf can also alert server admin with script that is sending spam. With out knowing which script sending spam, it is not easy do prevent the spam mails. Checking web site access log can give some idea.