Since the 11 September 2001 attacks and naming of the airport as a terrorism target by the Jemaah Islamiyah, the airport's security has been stepped up. Roving patrol teams consisting of SAF and SPF officers, armed with assault rifles or sub-machine guns, patrol the terminals at random intervals.[21] Officers from the Gurkha Contingent are also deployed to patrol the transit areas of the terminal buildings. These measures come at a cost partly borne by travellers in the form of a "passenger security service charge," imposed since 2002.