A terminal device obtains location information relating to its location, wherein the location information comprises first location information and second location information, wherein the first location information relates to a location of the terminal device within a region, and wherein the second location information identifies the region in which the terminal device is located. The terminal device forms content for a proximity service discovery message, wherein the content for the discovery message includes the first location information; calculates a message integrity code based on the content for the discovery message and the second location information; and transmits the proximity service discovery message, comprising the content for the discovery message and the computed message integrity code.