Computer test used in diagnostic: apt challenge (7)

I believe the answer is:

captcha

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'computer test' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'in diagnostic apt challenge' is the wordplay.
'in' indicates a hidden word.
'CAPTCHA' is hidden in the letters of 'diagnostic apt challenge'.

'used' is the link.

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(Another definition for captcha that I've seen is " E-security feature".)

I've seen this clue in The Times.

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