Here's the abstract of the study linked above (there have been other studies too):
The German Dunkelfeld Project: A Pilot Study to Prevent Child Sexual Abuse and the Use of Child Abusive Images
Klaus M. Beier MD, PhD,
Dorit Grundmann MSc,
Laura F. Kuhle MSc,
Gerold Scherner MSc,
Anna Konrad MSc and
Till Amelung MD*
Article first published online: 4 DEC 2014
© 2014 International Society for Sexual Medicine
Cover image for Vol. 11 Issue 12 The Journal of Sexual Medicine
Child Sexual Abuse;
Child Abusive Images
Sexual interest toward prepubescents and pubescents (pedophilia and hebephilia) constitutes a major risk factor for child sexual abuse (CSA) and viewing of child abusive images, i.e., child pornography offenses (CPO). Most child sexual exploitation involving CSA and CPO are undetected and unprosecuted in the “Dunkelfeld” (German: “dark field”).
This study assesses a treatment program to enhance behavioral control and reduce associated dynamic risk factors (DRF) in self-motivated pedophiles/hebephiles in the Dunkelfeld.
Between 2005 and 2011, 319 undetected help-seeking pedophiles and hebephiles expressed interest in taking part in an anonymous and confidential 1-year-treatment program using broad cognitive behavioral methodology in the Prevention Project Dunkelfeld. Therapy was assessed using nonrandomized waiting list control design (n = 53 treated group [TG]; n = 22 untreated control group [CG]).
Main Outcome Measures
Self-reported pre-/posttreatment DRF changes were assessed and compared with CG. Offending behavior characteristics were also assessed via self-reporting.
No pre-/postassessment changes occurred in the control group. Emotional deficits and offense-supportive cognitions decreased in the TG; posttherapy sexual self-regulation increased. Treatment-related changes were distributed unequally across offender groups. None of the offending behavior reported for the TG was identified as such by the legal authorities. However, five of 25 CSA offenders and 29 of 32 CPO offenders reported ongoing behaviors under therapy.
Therapy for pedophiles/hebephiles in the Dunkelfeld can alter child sexual offending DRF and reduce-related behaviors. Unidentified, unlawful child sexual exploitative behaviors are more prevalent in this population than in officially reported recidivism. Further research into factors predictive of problematic sexual behaviors in the Dunkelfeld is warranted.
Beier KM, Grundmann D, Kuhle LF, Scherner G, Konrad A, and Amelung T. The German Dunkelfeld Project: A pilot study to prevent child sexual abuse and the use of child abusive images. J Sex Med **;**:**–**.
Yes, it's not clear what "ongoing behaviours" means in the abstract - could be anything from actual offending to masturbation.
But at this point any treatment is better than NO treatment. These are mostly self-identified men, who are uncomfortable about their orientation - uncomfortable enough to contact the treaters voluntarily and attend for treatment.
I don't think the project in UCC continued beyond the principal researchers leaving to go to another university - I may be wrong though.