The objective of this feasibility study is to evaluate the feasibility, acceptability, and potential usefulness of the investigational device, a mobile software application (app) (OC Free) for treatment of OCD (contamination obsession only), adjunctive to individuals receiving outpatient ERP therapy. OC Free is an iOS/Android app that provides treatment via computerized exposure and response prevention (ERP). The study will evaluate preliminary safety and effectiveness of the app using gold-standard, validated 'clinician-administered' and 'self-reporting measures.'