Referring to the link Anthony provided, at minimum I would recommend applying this security update:

* 9.00.50572005.90.5057.02494120 MS11-049: Description of the security update for SQL Server 2005 Service Pack 4 GDR: June 14, 2011

Ideally I would recommend applying CU3 and everything newer than that (listed from newest to oldest, but apply from oldest to newest):

* 9.00.53242005.90.5324.02716427 MS12-070: Description of the security update for SQL Server 2005 Service Pack 4 QFE

* 9.00.52962005.90.5296.02615425 FIX: "Msg 7359" error when a view uses another view in SQL Server 2005 if the schema version of a remote table is updated

* 9.00.52952005.90.5295.02598903 FIX: SQL Server Agent job randomly stops when you schedule the job to run past midnight on specific days in SQL Server 2005, in SQL Server 2008 or in SQL Server 2008 R2

* 9.00.52942005.90.5294.02572407 FIX: Error 5180 when you use the ONLINE option to rebuild an index in SQL Server 2005

* 9.00.52922005.90.5292.02494123 MS11-049: Description of the security update for SQL Server 2005 Service Pack 4 GDR: June 14, 2011

* 9.00.52662005.90.5266.02507769 Cumulative update package 3 (CU3) for SQL Server 2005 Service Pack 4