Your opponents and creatures your opponents control donâ€™t actually lose hexproof, although you will ignore hexproof for purposes of choosing targets of spells and abilities you control.
Creatures your opponents control with â€œhexproof from [quality]â€ abilities can be targeted as though they didnâ€™t have those abilities as well.
Because Detection Towerâ€™s last ability doesnâ€™t change the characteristics of any permanents, the set of creatures affected by it is constantly updated. Creatures that come under your opponentsâ€™ control later in the turn can be targeted as though they didnâ€™t have hexproof.
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