Unknown users in dba_users

I just checked the contents of the dba_users table and found an unknown user: 'AURORA$ORB$UNAUTHENTICATED'. This was created quite recently. I am the only dba and cant think of any process or modification that may have made this entry. Has anyone encountered a similar problem?

that user is created by Oracle for JServer in 8i

cheers pando, I thought I had a hacker for a minute.