As you seem to know, all the choices given in the exercise (targeted, aimed, directed, and pointed) are verbs. The tricky part is which verb is the correct answer, right?
This exercise question seems to have two goals: meaning, and syntax.
A good dictionary should be handy, not just in this specific exercise question, but in other questions you may find in the future, too. Here are some relevant definitions given by Macmillan Dictionary:
target: 1 to intend or to try to attack someone or something
3 to criticize or to work against a particular person or group that you oppose
Police are specifically targeting criminal gangs.
aim: 1 to point a gun or an object you are throwing at something that you want to hit
aim at/for: He was aiming at the tree but he missed.
direct: 5 to tell or show someone the way to a place or where to go by giving them instructions or by pointing
direct someone to something: Could you direct me to the bus station?
point: 3 to aim an object at someone or something
point something at/toward someone/something: He pointed his rifle at the deer and pulled the trigger.
As you can see, we direct someone to a destination; we don't direct a destination. Saying The police directed 2100 alleged up-loaders using peer-to-peer doesn't make much sense, unless the police already have those up-loaders in custody. This rules out directed.
Let's consider aim and point next. We aim/point something at a target; we don't aim/point the target. Saying The police aimed/pointed 2100 such up-loaders doesn't make sense. (Though The police aimed at 2100 such up-loaders would.) This rules out aimed and pointed.
We have only one choice left, targeted. We target a target, and saying Police targeted 2100 such up-loaders makes sense. So, targeted is the answer.
Hope this helps!