APK security

Well, sort of. What proguard does is takes code such as

package com.mygamecompany.mygame.enemy;

class Enemy {
private int health;
private float x;
private float y;

public void fireAtPlayer()...
}

and turns it into something like

package a.b.c.d;

class A {
private int a;
private float b;
private float c;

public void d()...
}

The code will still run, but deciphering what most of it means will take while, particularly if the code is badly written to begin with.

Proguard also won't obfuscate any strings in the code, you can get commercial obfuscators which will do this though.