On the other hand, citizens should be required to register to vote abroad, or should be automatically registered. If voters are allowed to vote abroad without pre-registration and, at the same time, are included on in-country voter lists, such an arrangement creates the risk for multiple voting. This was cause of concern, for instance, in the Bulgarian 2017 elections. Where online registration for voting abroad is possible, like in Spain, special security measures have to been taken to protect data (transmission).