A player commits a crime as they cast a spell, activate an ability, or put a triggered ability on the stack that targets at least one opponent, at least one permanent, spell, or ability an opponent controls, and/or at least one card in an opponent’s graveyard.

When you proliferate, you can choose any permanent that has a counter, including ones controlled by opponents. You can choose any player who has a counter, including opponents. You can’t choose cards in any zone other than the battlefield, even if they have counters on them.

You don’t have to choose every permanent or player that has a counter—only the ones you want to add counters to. Since “any number” includes zero, you don’t have to choose any permanents at all, and you don’t have to choose any players at all.

Changing the target or targets of a spell or ability won’t affect whether the controller of that spell or ability has committed a crime. Only the initial targets chosen for that spell or ability are used to determine whether its controller committed a crime.

The spell or ability that constituted a crime doesn’t have to have resolved yet or at all. As soon as you’re finished casting the spell, activating the ability, or putting the triggered ability on the stack, you’ve committed a crime.

A player can commit only one crime per spell or ability they control. Targeting multiple opponents, permanents, spells, abilities, and/or cards with the same spell or ability doesn’t constitute committing multiple crimes.

Players can respond to a spell or ability whose effect includes proliferating. Once that spell or ability starts to resolve, however, and its controller chooses which permanents and players will get new counters, it’s too late for anyone to respond.

For example, an ability that triggers when you cast a spell that targets an opponent will trigger at the same time as an ability that triggers whenever you commit a crime. Those abilities can be put on the stack in either order (if you control them both), and they’ll both resolve before the spell that caused them to trigger.

If a permanent or player has more than one kind of counter on them, and you choose for that permanent or player to get additional counters, that permanent or player must get one of each kind of counter they already have. You can’t have them get just one kind of counter they already have and not the others.