Looks like my qmail server is being used to send spam

My qmail queue is filling up with what looks like spam emails to yahoo and hotmail accounts. These are not being sent by any of the domains listed in rcpthosts. How can I find out the ip of the person doing this and block them?
I have cleared the queue and tried killall qmail-remote but the q will soon start to fill up again.
I have also tried telnet relay-test.mail-abuse.org and it appears that any email containing the server hostname is allowable. I also need to stop this.
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Try running virus scans.
kirkheaton25Author Commented:
I have changed firewall settings and blocked the servers which were causing the problem.  I am now closing this question.

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Email Servers

From novice to tech pro — start learning today.