*They are not illegal aliens.An action is illegal.
A person who breaks the law isn't called an illegal, he or she is called a criminal.
They are criminal aliens.
Or foreign invaders ....
“Illegal alien” is the legal term as defined in the US Code.
They are criminal aliens.
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Criminal aliens from outer country. Which is somewhat different from criminal aliens from outer space.
The differences are mostly cosmetic and distances traveled to commit their criminal trespass.