Doing this turned out to be quite simple. The sensors have their own table in the database and one of the fields for a sensor is called ‘active’. I figured deactivating the sensors would do it. Deactivating all sensors from the net_name group ‘utrecht’ is done like this:

mysql> UPDATE sensor SET active=”N” WHERE net_name=”utrecht”;

After this, the net_name ‘utrecht’ disappeared from the Sguil client ‘Select Network(s) to Monitor’ screen. However, the ‘Agent Status’ tab in the Sguil client still showed the deactivated agents. This was solved by restarting the Sguil server. So now my ‘Agent Status’ list is clean again!