The most common and most likely answer to this crossword clue is the 8 letter word INVADERS
I've seen this crossword clue in The Daily Telegraph
I
N
V
A
D
E
R
S
More clues leading to the result INVADERS
- Aliens endlessly turned around these days
- Unwelcome visitors disturbed maidservant putting out mat
- Assailants wearing boots, as Klaus might say
- Violent illegal immigrants? Almost the opposite around outskirts of Auckland
- Those who occupy dives ran to get drunk
- Inches around Darth and Storm Troopers, perhaps
- Attackers damage hired vans, wanting hospital
- 1d
Buddy explains!

The straight part
We know that "Violent illegal immigrants" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case violent illegal immigrants = invaders.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does INVADERS mean?
INVADERS noun- One who invades a region
- An intruder (especially on someone's privacy)