Maybe activity in the main secure: daughter browsing the Net (11)

I believe the answer is:

windsurfing

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'maybe activity in the main' is the definition.
I can't judge whether this definition defines the answer.

'secure daughter browsing the net' is the wordplay.
'secure' becomes 'win' (I've seen this in other clues).
'daughter' becomes 'd' (genealogical abbreviation).
'browsing the net' becomes 'surfing' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'win'+'d'+'surfing'='WINDSURFING'

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I've seen this clue in The Times.

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