Every Swedish citizen and resident has a unique and dedicated number (date of birth followed by four digits), and you can use it in tandem with for example BankID (https://en.wikipedia.org/wiki/BankID) to authenticate yourself almost everywhere.
It would be extraordinarily hard to make up UBI claims for non-existing family members and receive payouts in Sweden. You would first have to convince the tax agency to register the fake person in order to get a new personal number, either as a newborn or immigrant, which either way is obviously subject to controls. You’d then have to keep this up through various mandatory interactions with government agencies without getting found out. It would probably be much more effort (not to mention stress) than just working for the same money.
There are special protections for illegal immigrants so it's reasonably easy to invent a family of them to collect benefits.
In addition, various US govts or even agencies within the same govt, often don't talk to one another.
So, when an old person dies, friends/family can keep collecting benefits.
See https://www.theguardian.com/money/2015/mar/16/social-securit...
"Social Security records show that 6.5 million people in the US have reached the ripe old age of 112. In reality, only few could possibly be alive. As of last fall, there were only 42 people known to be that old in the entire world."
It's not just dead people.
"One Social Security number was used 613 times. An additional 194 numbers were used at least 50 times each."
Which, one again, circles to the point that the money, time, and effort spent on fighting such low level individual fraud typically vastly out-spends the actual fraud they're trying to combat.
