Cryptic crossword clue
Julius is sent a computer test message, which was an encroachment 8

The most common and most likely answer to this crossword clue is the 8 letter word IMPINGED

I've seen this crossword clue in Financial Times
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Buddy explains!

The straight part
We know that "was an encroachment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case was an encroachment = impinged.
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 IMPINGED mean?

IMPINGED verb
  1. To make a physical impact on.
  2. To interfere with.
  3. To have an effect upon, especially a negative one.

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