Have not done one personally, but a couple of peeps have to do theirs every 24 month, or their security clearance gets revoked. I am their "reference" and get a visit from SSA to verify their information . The questions range from finance to their sexuality ... preferred self medication substance ... , known properties, bad personality traits...listed self identified vices, - that could possibly open them to black mailing. Invasive indeed , but if there is nothing to hide, why would you, referencing said Eskom managers here, not just get it over and done with. With all the kak that goes on at Eskom...I would say, they do have something to hide.