A huge security whole was just discovered in all 4.5 versions of Mambo.
Security patches for v4.5.1a and 4.5-1.0.9 have just been released and are available at http://mamboforge.net/frs/?group_id=5
It is recommended to patch ALL installations ASAP to avoid compromising your whole server.
For more information: http://forum.mamboserver.com/showthread.php?p=146550