393642 Remove virus or script

We have noticed that spam emails are being sent to people using differentnames at [login to view URL] The "from" email addresses do not exist as pop3 email addresses on our server and we suspect that someone who worked on our server recently must have inserted a script / virus to send out these spam emails and making it seem as if the emails are coming from someone in our employ / service. We are looking for someone to urgently fix this issue by removing the script or the virus.