exim log - nobody

hi, i got this email and it is some sort of spam.. i think someone is using my server to spam people. Anyone have any idea what it means? 2004-04-27 15:16:47 1BIZ0Z-0004Mt-Vz <= tguajar@xxx.com U=nobody P=local S=673 2004-04-27 15:16:48 1BIZ0Z-0004Mt-Vz => tsteele@xxx.com R=lookuphost T=remote_smtp H=utc.univ-coop.austin.tx.us [198.xxx.xxx.x] 2004-04-27 15:16:48 1BIZ0Z-0004Mt-Vz Completed Looks like the user used nobody as login and locally sent the message to tsteele.. Is that right? thanks henry