Paranoia, the belief that you are at risk of significant physical or emotional harm from others, is a common difficulty, which causes significant distress and impairment to daily functioning, including in psychosis-spectrum disorders. According to cognitive models of psychosis, paranoia may be partly maintained by cognitive processes, including interpretation biases. Cognitive bias modification for paranoia (CBM-pa) is an intervention targeting the bias towards interpreting ambiguous social scenarios in a way that is personally threatening. This study aims to test the efficacy and safety of a mobile app version of CBM-pa, called STOP (successful treatment of paranoia).