I am reading the fate core rule book, and it says "just knowing someone is typically not enough to hurt someone." Yet, depending on the type of game you're playing, if you're dealing with a gang, the mafia, or some other underground organization - or even a corrupt governmental institutions, sometimes a single word to "take care of someone" can have someone put down. Or would that be put under a different type of an aspect?
Using the Contacts skill to attack is something that you'll have to determine as a group. Consider the following advice from Judging the Use of Skills and Stunts (Fate SRD):
The only other major problem you’ll have to worry about is when you run into an “edge case” with a skill—a player wants to use it for an action that seems like a bit of a stretch, or a situation comes up in your game where it makes sense to use a skill for something that’s not normally a part of its description.
When you run into this, talk it over with the group and see what everyone thinks. It’s going to end up one of three ways:
— It’s too much of a stretch. Consider creating a new skill.
— It’s not a stretch, and anyone can use the skill that way from now on under the same conditions.
— It wouldn’t be a stretch if the character had a stunt that allowed it.