Securing in-app purchases

A non-transitory machine readable medium storing executable instructions which when executed by a data processing system cause the data processing system to perform a method of providing purchases through an application purchased from an online store, the method comprising:

• receiving, at a device, a request within the application to purchase an asset for use with the application which is produced by an application vendor;
• transmitting the request and a vendor identifier associated with the application vendor to the on-line store;
• receiving a signed receipt from the on-line store, the signed receipt including data derived from the vendor identifier, the signed receipt being signed by an operator of the on-line store;
• verifying the signed receipt by comparing a vendor identifier obtained from the signed receipt to the vendor identifier of the application vendor.