be kept by the ticket controller. Whether or not one can leave and reenter with the customer's ticket stub only varies. It may not be allowed to avoid subsequent use of one ticket by multiple people, or even simultaneous use by giving the ticket to someone before the ticket check (if this is physically possible), but it may also be allowed, e.g., in a movie theatre to allow the stub holder to use the facilities (restroom, telephone, water fountain) or buy, during a movie, a snack or drink before the ticket check and reenter. A ticket may be printed in advance, or fully or partly printed when issued, or it may be a printed form that is completed in handwriting (e.g., by a train conductor who does not carry a ticket machine, but just a supply of forms and a pen). Security issues Counterfeit tickets are a problem at high-priced concerts and other events, so holograms are used on tickets for the FIFA World Cup, Olympic Games, Super Bowl, and other high-profile events. The fraudulent practice of passing-back a ticket can be overcome by making the ticket in the form of a tamper-proof wristband. When paying online for admission one may get a code, or a ticket that can be printed out, or shown on one's mobile device to be scanned or verified by the ticket taker. At the premises, it is made sure that the same right of admission is not used by other parties. Internet ticket fraud has become widespread, with authentic-looking but fake ticket websites taking customers' money but not delivering the tickets, notably for the 2008 Beijing Olympic Games (through websites not based in China). Virtual queueing Free tickets are applied in virtual queueing. In a place where one has to wait one's turn, there may be the system that one takes a ticket with a number from a dispenser. This system is usually found in hospitals and surgeries, and at offices where many people visit, like town halls, social security offices, labor exchanges, or post offices. Another form of virtual queuing is where the ticket carries a time-slot on it, rather than just a sequentially incremented number. This type of ticket would allow someone to do other things and then return for a roller-coaster ride, for example, without having to actually stand and wait in line. NFT ticketing NFT (non-fungible token) ticketing is an innovation