As described in OPC 10000-4, the FindServersOnNetwork Service can be used without security and is therefore vulnerable to denial of service (DOS) attacks. A Discovery Server should minimize the amount of processing required to send the response for this Service. This can be achieved by preparing the result in advance.
The GDS only accept Server registrations from Servers that are trusted or have appropriate administrative access rights. This will help ensure that a rogue Server does not become registered with a GDS.