The Immigration Department has confirmed Greens senator Sarah Hanson-Young was spied on during her visit to Nauru by at least one Wilson Security officer who may have had a "brain explosion".

This directly contradicts comments by Immigration Minister Peter Dutton, who said last week that the spying claims were "complete nonsense", labelling Senator Hanson-Young as an "embarrassment to this country".

Greens senator Sarah Hanson-Young referred the office of former Immigration Minister Scott Morrison over the alleged release of Nauru information to a journalist. Credit:Andrew Meares

But in evidence given on Tuesday to a parliamentary inquiry into allegations of abuse at the Nauruan centre, department secretary Michael Pezzullo confirmed that at least one Wilson security staff member had trailed Senator Hanson-Young's car during her visit to Nauru in December 2013 and had since been disciplined.