Each voting place knows exactly who may turn up to vote (they cross you out on a list, when you collect your ballot), so stuffing the ballot boxes is difficult.
Cheating is of course always possible, but only locally and in small numbers.
Edit: Having phantom voters is not possible. Big Brother knows exactly who is legally allowed to vote, and that list is distributed to each voting place. If you are illegally in the country, you don't exist on the voter roles.
Each voting place knows exactly who may turn up to vote (they cross you out on a list, when you collect your ballot), so stuffing the ballot boxes is difficult.
Cheating is of course always possible, but only locally and in small numbers.
Edit: Having phantom voters is not possible. Big Brother knows exactly who is legally allowed to vote, and that list is distributed to each voting place. If you are illegally in the country, you don't exist on the voter roles.