Yahoo email spam issues. Virus on specific computer or something else?

Most of the time i am on a work computer i hardly use my home computer. I recently found out that my yahoo email is sending ppl in my contacts list spam. My home computer has virus protection (AVG) and work computer has McAfee which is scanned by IT people periodically but i dont know if mcafee helps or not b/c i cant do a scan myself. We would have to request a scan from the IT ppl. I have done everything else that i can think of to prevent beforehand and stop after i found out. The work computer is the one i think might have a virus but i dont know if this is this a virus on a specific computer or is this something that i would have to fix in my email account? Any suggestions would greatly help....I need my yahoo email to stop sending ppl spam T^T