SQL Server Agent jobs are protected by SQL Server security. From BOL:
Members of the SQLAgentUserRole, SQLAgentReaderRole, and SQLAgentOperatorRole fixed database roles in msdb, and members of the sysadmin fixed server role have access to SQL Server Agent. A user that does not belong to any of these roles cannot use SQL Server Agent. For more information on the roles used by SQL Server Agent, see Implementing SQL Server Agent Security.